19 The Global Object

The global object:

is created before control enters any execution context.
does not have a [[Construct]] internal method; it cannot be used as a constructor with the new operator.
does not have a [[Call]] internal method; it cannot be invoked as a function.
has a [[Prototype]] internal slot whose value is host-defined.
may have host-defined properties in addition to the properties defined in this specification. This may include a property whose value is the global object itself.

19.1 Value Properties of the Global Object

19.1.1 globalThis

The initial value of the "globalThis" property of the global object in a Realm Record realm is realm.[[GlobalEnv]].[[GlobalThisValue]].

This property has the attributes { [[Writable]]: true, [[Enumerable]]: false, [[Configurable]]: true }.

19.1.2 Infinity

The value of Infinity is +∞_𝔽 (see 6.1.6.1). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

19.1.3 NaN

The value of NaN is NaN (see 6.1.6.1). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

19.1.4 undefined

The value of undefined is undefined (see 6.1.1). This property has the attributes { [[Writable]]: false, [[Enumerable]]: false, [[Configurable]]: false }.

19.2 Function Properties of the Global Object

19.2.1 eval ( `x` )

The eval function is the %eval% intrinsic object. When the eval function is called with one argument x, the following steps are taken:

Assert: The execution context stack has at least two elements.
Let callerContext be the second to top element of the execution context stack.
Let callerRealm be callerContext's Realm.
Return ? PerformEval(x, callerRealm, false, false).

19.2.1.1 PerformEval ( `x`, `callerRealm`, `strictCaller`, `direct` )

The abstract operation PerformEval takes arguments x, callerRealm, strictCaller, and direct and returns either a normal completion containing an ECMAScript language value or an abrupt completion. It performs the following steps when called:

Assert: If direct is false, then strictCaller is also false.
If Type(x) is not String, return x.
Let evalRealm be the current Realm Record.
Perform ? HostEnsureCanCompileStrings(callerRealm, evalRealm).
Let inFunction be false.
Let inMethod be false.
Let inDerivedConstructor be false.
Let inClassFieldInitializer be false.
If direct is true, then
1. Let thisEnvRec be GetThisEnvironment().
2. If thisEnvRec is a function Environment Record, then
  1. Let F be thisEnvRec.[[FunctionObject]].
  2. Set inFunction to true.
  3. Set inMethod to thisEnvRec.HasSuperBinding().
  4. If F.[[ConstructorKind]] is derived, set inDerivedConstructor to true.
  5. Let classFieldIntializerName be F.[[ClassFieldInitializerName]].
  6. If classFieldIntializerName is not empty, set inClassFieldInitializer to true.
Perform the following substeps in an implementation-defined order, possibly interleaving parsing and error detection:
1. Let script be ParseText(StringToCodePoints(x), Script).
2. If script is a List of errors, throw a SyntaxError exception.
3. If script Contains ScriptBody is false, return undefined.
4. Let body be the ScriptBody of script.
5. If inFunction is false, and body Contains NewTarget, throw a SyntaxError exception.
6. If inMethod is false, and body Contains SuperProperty, throw a SyntaxError exception.
7. If inDerivedConstructor is false, and body Contains SuperCall, throw a SyntaxError exception.
8. If inClassFieldInitializer is true, and ContainsArguments of body is true, throw a SyntaxError exception.
If strictCaller is true, let strictEval be true.
Else, let strictEval be IsStrict of script.
Let runningContext be the running execution context.
NOTE: If direct is true, runningContext will be the execution context that performed the direct eval. If direct is false, runningContext will be the execution context for the invocation of the eval function.
If direct is true, then
1. Let lexEnv be NewDeclarativeEnvironment(runningContext's LexicalEnvironment).
2. Let varEnv be runningContext's VariableEnvironment.
3. Let privateEnv be runningContext's PrivateEnvironment.
Else,
1. Let lexEnv be NewDeclarativeEnvironment(evalRealm.[[GlobalEnv]]).
2. Let varEnv be evalRealm.[[GlobalEnv]].
3. Let privateEnv be null.
If strictEval is true, set varEnv to lexEnv.
If runningContext is not already suspended, suspend runningContext.
Let evalContext be a new ECMAScript code execution context.
Set evalContext's Function to null.
Set evalContext's Realm to evalRealm.
Set evalContext's ScriptOrModule to runningContext's ScriptOrModule.
Set evalContext's VariableEnvironment to varEnv.
Set evalContext's LexicalEnvironment to lexEnv.
Set evalContext's PrivateEnvironment to privateEnv.
Push evalContext onto the execution context stack; evalContext is now the running execution context.
Let result be Completion(EvalDeclarationInstantiation(body, varEnv, lexEnv, privateEnv, strictEval)).
If result.[[Type]] is normal, then
1. Set result to the result of evaluating body.
If result.[[Type]] is normal and result.[[Value]] is empty, then
1. Set result to NormalCompletion(undefined).
Suspend evalContext and remove it from the execution context stack.
Resume the context that is now on the top of the execution context stack as the running execution context.
Return ? result.

Note

The eval code cannot instantiate variable or function bindings in the variable environment of the calling context that invoked the eval if either the code of the calling context or the eval code is strict mode code. Instead such bindings are instantiated in a new VariableEnvironment that is only accessible to the eval code. Bindings introduced by let, const, or class declarations are always instantiated in a new LexicalEnvironment.

19.2.1.2 HostEnsureCanCompileStrings ( `callerRealm`, `calleeRealm` )

The host-defined abstract operation HostEnsureCanCompileStrings takes arguments callerRealm (a Realm Record) and calleeRealm (a Realm Record) and returns either a normal completion containing unused or an abrupt completion. It allows host environments to block certain ECMAScript functions which allow developers to compile strings into ECMAScript code.

An implementation of HostEnsureCanCompileStrings must conform to the following requirements:

If the returned Completion Record is a normal completion, it must be a normal completion containing unused.

The default implementation of HostEnsureCanCompileStrings is to return NormalCompletion(unused).

19.2.1.3 EvalDeclarationInstantiation ( `body`, `varEnv`, `lexEnv`, `privateEnv`, `strict` )

The abstract operation EvalDeclarationInstantiation takes arguments body, varEnv, lexEnv, privateEnv, and strict and returns either a normal completion containing unused or an abrupt completion. It performs the following steps when called:

Let varNames be the VarDeclaredNames of body.
Let varDeclarations be the VarScopedDeclarations of body.
If strict is false, then
1. If varEnv is a global Environment Record, then
  1. For each element name of varNames, do
    1. If varEnv.HasLexicalDeclaration(name) is true, throw a SyntaxError exception.
    2. NOTE: eval will not create a global var declaration that would be shadowed by a global lexical declaration.
2. Let thisEnv be lexEnv.
3. Assert: The following loop will terminate.
4. Repeat, while thisEnv is not the same as varEnv,
  1. If thisEnv is not an object Environment Record, then
    1. NOTE: The environment of with statements cannot contain any lexical declaration so it doesn't need to be checked for var/let hoisting conflicts.
    2. For each element name of varNames, do
      1. If ! thisEnv.HasBinding(name) is true, then
        Throw a SyntaxError exception.
        NOTE: Annex B.3.4 defines alternate semantics for the above step.
      2. NOTE: A direct eval will not hoist var declaration over a like-named lexical declaration.
  2. Set thisEnv to thisEnv.[[OuterEnv]].
Let privateIdentifiers be a new empty List.
Let pointer be privateEnv.
Repeat, while pointer is not null,
1. For each Private Name binding of pointer.[[Names]], do
  1. If privateIdentifiers does not contain binding.[[Description]], append binding.[[Description]] to privateIdentifiers.
2. Set pointer to pointer.[[OuterPrivateEnvironment]].
If AllPrivateIdentifiersValid of body with argument privateIdentifiers is false, throw a SyntaxError exception.
Let functionsToInitialize be a new empty List.
Let declaredFunctionNames be a new empty List.
For each element d of varDeclarations, in reverse List order, do
1. If d is neither a VariableDeclaration nor a ForBinding nor a BindingIdentifier, then
  1. Assert: d is either a FunctionDeclaration, a GeneratorDeclaration, an AsyncFunctionDeclaration, or an AsyncGeneratorDeclaration.
  2. NOTE: If there are multiple function declarations for the same name, the last declaration is used.
  3. Let fn be the sole element of the BoundNames of d.
  4. If fn is not an element of declaredFunctionNames, then
    1. If varEnv is a global Environment Record, then
      1. Let fnDefinable be ? varEnv.CanDeclareGlobalFunction(fn).
      2. If fnDefinable is false, throw a TypeError exception.
    2. Append fn to declaredFunctionNames.
    3. Insert d as the first element of functionsToInitialize.
NOTE: Annex B.3.2.3 adds additional steps at this point.
Let declaredVarNames be a new empty List.
For each element d of varDeclarations, do
1. If d is a VariableDeclaration, a ForBinding, or a BindingIdentifier, then
  1. For each String vn of the BoundNames of d, do
    1. If vn is not an element of declaredFunctionNames, then
      1. If varEnv is a global Environment Record, then
        Let vnDefinable be ? varEnv.CanDeclareGlobalVar(vn).
        If vnDefinable is false, throw a TypeError exception.
      2. If vn is not an element of declaredVarNames, then
        Append vn to declaredVarNames.
NOTE: No abnormal terminations occur after this algorithm step unless varEnv is a global Environment Record and the global object is a Proxy exotic object.
Let lexDeclarations be the LexicallyScopedDeclarations of body.
For each element d of lexDeclarations, do
1. NOTE: Lexically declared names are only instantiated here but not initialized.
2. For each element dn of the BoundNames of d, do
  1. If IsConstantDeclaration of d is true, then
    1. Perform ? lexEnv.CreateImmutableBinding(dn, true).
  2. Else,
    1. Perform ? lexEnv.CreateMutableBinding(dn, false).
For each Parse Node f of functionsToInitialize, do
1. Let fn be the sole element of the BoundNames of f.
2. Let fo be InstantiateFunctionObject of f with arguments lexEnv and privateEnv.
3. If varEnv is a global Environment Record, then
  1. Perform ? varEnv.CreateGlobalFunctionBinding(fn, fo, true).
4. Else,
  1. Let bindingExists be ! varEnv.HasBinding(fn).
  2. If bindingExists is false, then
    1. NOTE: The following invocation cannot return an abrupt completion because of the validation preceding step 14.
    2. Perform ! varEnv.CreateMutableBinding(fn, true).
    3. Perform ! varEnv.InitializeBinding(fn, fo).
  3. Else,
    1. Perform ! varEnv.SetMutableBinding(fn, fo, false).
For each String vn of declaredVarNames, do
1. If varEnv is a global Environment Record, then
  1. Perform ? varEnv.CreateGlobalVarBinding(vn, true).
2. Else,
  1. Let bindingExists be ! varEnv.HasBinding(vn).
  2. If bindingExists is false, then
    1. NOTE: The following invocation cannot return an abrupt completion because of the validation preceding step 14.
    2. Perform ! varEnv.CreateMutableBinding(vn, true).
    3. Perform ! varEnv.InitializeBinding(vn, undefined).
Return unused.

Note

An alternative version of this algorithm is described in B.3.4.

19.2.2 isFinite ( `number` )

The isFinite function is the %isFinite% intrinsic object. When the isFinite function is called with one argument number, the following steps are taken:

Let num be ? ToNumber(number).
If num is NaN, +∞_𝔽, or -∞_𝔽, return false.
Otherwise, return true.

19.2.3 isNaN ( `number` )

The isNaN function is the %isNaN% intrinsic object. When the isNaN function is called with one argument number, the following steps are taken:

Let num be ? ToNumber(number).
If num is NaN, return true.
Otherwise, return false.

Note

A reliable way for ECMAScript code to test if a value X is a NaN is an expression of the form X !== X. The result will be true if and only if X is a NaN.

19.2.4 parseFloat ( `string` )

The parseFloat function produces a Number value dictated by interpretation of the contents of the string argument as a decimal literal.

The parseFloat function is the %parseFloat% intrinsic object. When the parseFloat function is called with one argument string, the following steps are taken:

Let inputString be ? ToString(string).
Let trimmedString be ! TrimString(inputString, start).
If neither trimmedString nor any prefix of trimmedString satisfies the syntax of a StrDecimalLiteral (see 7.1.4.1), return NaN.
Let numberString be the longest prefix of trimmedString, which might be trimmedString itself, that satisfies the syntax of a StrDecimalLiteral.
Let parsedNumber be ParseText(StringToCodePoints(numberString), StrDecimalLiteral).
Assert: parsedNumber is a Parse Node.
Return StringNumericValue of parsedNumber.

Note

parseFloat may interpret only a leading portion of string as a Number value; it ignores any code units that cannot be interpreted as part of the notation of a decimal literal, and no indication is given that any such code units were ignored.

19.2.5 parseInt ( `string`, `radix` )

The parseInt function produces an integral Number dictated by interpretation of the contents of the string argument according to the specified radix. Leading white space in string is ignored. If radix is undefined or 0, it is assumed to be 10 except when the number begins with the code unit pairs 0x or 0X, in which case a radix of 16 is assumed. If radix is 16, the number may also optionally begin with the code unit pairs 0x or 0X.

The parseInt function is the %parseInt% intrinsic object. When the parseInt function is called, the following steps are taken:

Let inputString be ? ToString(string).
Let S be ! TrimString(inputString, start).
Let sign be 1.
If S is not empty and the first code unit of S is the code unit 0x002D (HYPHEN-MINUS), set sign to -1.
If S is not empty and the first code unit of S is the code unit 0x002B (PLUS SIGN) or the code unit 0x002D (HYPHEN-MINUS), remove the first code unit from S.
Let R be ℝ(? ToInt32(radix)).
Let stripPrefix be true.
If R ≠ 0, then
1. If R < 2 or R > 36, return NaN.
2. If R ≠ 16, set stripPrefix to false.
Else,
1. Set R to 10.
If stripPrefix is true, then
1. If the length of S is at least 2 and the first two code units of S are either "0x" or "0X", then
  1. Remove the first two code units from S.
  2. Set R to 16.
If S contains a code unit that is not a radix-R digit, let end be the index within S of the first such code unit; otherwise, let end be the length of S.
Let Z be the substring of S from 0 to end.
If Z is empty, return NaN.
Let mathInt be the integer value that is represented by Z in radix-R notation, using the letters A-Z and a-z for digits with values 10 through 35. (However, if R is 10 and Z contains more than 20 significant digits, every significant digit after the 20th may be replaced by a 0 digit, at the option of the implementation; and if R is not 2, 4, 8, 10, 16, or 32, then mathInt may be an implementation-approximated integer representing the integer value denoted by Z in radix-R notation.)
If mathInt = 0, then
1. If sign = -1, return -0_𝔽.
2. Return +0_𝔽.
Return 𝔽(sign × mathInt).

Note

parseInt may interpret only a leading portion of string as an integer value; it ignores any code units that cannot be interpreted as part of the notation of an integer, and no indication is given that any such code units were ignored.

19.2.6 URI Handling Functions

Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or files) and transport protocols by which to access them (e.g. HTTP or FTP) on the Internet. The ECMAScript language itself does not provide any support for using URIs except for functions that encode and decode URIs as described in 19.2.6.2, 19.2.6.3, 19.2.6.4 and 19.2.6.5

Note

Many implementations of ECMAScript provide additional functions and methods that manipulate web pages; these functions are beyond the scope of this standard.

19.2.6.1 URI Syntax and Semantics

A URI is composed of a sequence of components separated by component separators. The general form is:

Scheme : First / Second ; Third ? Fourth

where the italicized names represent components and “:”, “/”, “;” and “?” are reserved for use as separators. The encodeURI and decodeURI functions are intended to work with complete URIs; they assume that any reserved code units in the URI are intended to have special meaning and so are not encoded. The encodeURIComponent and decodeURIComponent functions are intended to work with the individual component parts of a URI; they assume that any reserved code units represent text and so must be encoded so that they are not interpreted as reserved code units when the component is part of a complete URI.

The following lexical grammar specifies the form of encoded URIs.

Syntax

:::

opt

:::

opt

:::

:::

one of

;

:::

:::

:::

one of

uriMark

:::

one of

(

)

Note

The above syntax is based upon RFC 2396 and does not reflect changes introduced by the more recent RFC 3986.

Runtime Semantics

When a code unit to be included in a URI is not listed above or is not intended to have the special meaning sometimes given to the reserved code units, that code unit must be encoded. The code unit is transformed into its UTF-8 encoding, with surrogate pairs first converted from UTF-16 to the corresponding code point value. (Note that for code units in the range [0, 127] this results in a single octet with the same value.) The resulting sequence of octets is then transformed into a String with each octet represented by an escape sequence of the form "%xx".

19.2.6.1.1 Encode ( `string`, `unescapedSet` )

The abstract operation Encode takes arguments string (a String) and unescapedSet (a String) and returns either a normal completion containing a String or an abrupt completion. It performs URI encoding and escaping. It performs the following steps when called:

Let strLen be the number of code units in string.
Let R be the empty String.
Let k be 0.
Repeat,
1. If k = strLen, return R.
2. Let C be the code unit at index k within string.
3. If C is in unescapedSet, then
  1. Set k to k + 1.
  2. Set R to the string-concatenation of R and C.
4. Else,
  1. Let cp be CodePointAt(string, k).
  2. If cp.[[IsUnpairedSurrogate]] is true, throw a URIError exception.
  3. Set k to k + cp.[[CodeUnitCount]].
  4. Let Octets be the List of octets resulting by applying the UTF-8 transformation to cp.[[CodePoint]].
  5. For each element octet of Octets, do
    1. Set R to the string-concatenation of:
      - R
      - "%"
      - the String representation of octet, formatted as a two-digit uppercase hexadecimal number, padded to the left with a zero if necessary

19.2.6.1.2 Decode ( `string`, `reservedSet` )

The abstract operation Decode takes arguments string (a String) and reservedSet (a String) and returns either a normal completion containing a String or an abrupt completion. It performs URI unescaping and decoding. It performs the following steps when called:

Let strLen be the length of string.
Let R be the empty String.
Let k be 0.
Repeat,
1. If k = strLen, return R.
2. Let C be the code unit at index k within string.
3. If C is not the code unit 0x0025 (PERCENT SIGN), then
  1. Let S be the String value containing only the code unit C.
4. Else,
  1. Let start be k.
  2. If k + 2 ≥ strLen, throw a URIError exception.
  3. If the code units at index (k + 1) and (k + 2) within string do not represent hexadecimal digits, throw a URIError exception.
  4. Let B be the 8-bit value represented by the two hexadecimal digits at index (k + 1) and (k + 2).
  5. Set k to k + 2.
  6. Let n be the number of leading 1 bits in B.
  7. If n = 0, then
    1. Let C be the code unit whose value is B.
    2. If C is not in reservedSet, then
      1. Let S be the String value containing only the code unit C.
    3. Else,
      1. Let S be the substring of string from start to k + 1.
  8. Else,
    1. If n = 1 or n > 4, throw a URIError exception.
    2. If k + (3 × (n - 1)) ≥ strLen, throw a URIError exception.
    3. Let Octets be « B ».
    4. Let j be 1.
    5. Repeat, while j < n,
      1. Set k to k + 1.
      2. If the code unit at index k within string is not the code unit 0x0025 (PERCENT SIGN), throw a URIError exception.
      3. If the code units at index (k + 1) and (k + 2) within string do not represent hexadecimal digits, throw a URIError exception.
      4. Let B be the 8-bit value represented by the two hexadecimal digits at index (k + 1) and (k + 2).
      5. Set k to k + 2.
      6. Append B to Octets.
      7. Set j to j + 1.
    6. Assert: The length of Octets is n.
    7. If Octets does not contain a valid UTF-8 encoding of a Unicode code point, throw a URIError exception.
    8. Let V be the code point obtained by applying the UTF-8 transformation to Octets, that is, from a List of octets into a 21-bit value.
    9. Let S be UTF16EncodeCodePoint(V).
5. Set R to the string-concatenation of R and S.
6. Set k to k + 1.

Note

This syntax of Uniform Resource Identifiers is based upon RFC 2396 and does not reflect the more recent RFC 3986 which replaces RFC 2396. A formal description and implementation of UTF-8 is given in RFC 3629.

RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the invalid sequence C0 80 must not decode into the code unit 0x0000. Implementations of the Decode algorithm are required to throw a URIError when encountering such invalid sequences.

19.2.6.2 decodeURI ( `encodedURI` )

The decodeURI function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by the encodeURI function is replaced with the UTF-16 encoding of the code points that it represents. Escape sequences that could not have been introduced by encodeURI are not replaced.

The decodeURI function is the %decodeURI% intrinsic object. When the decodeURI function is called with one argument encodedURI, the following steps are taken:

Let uriString be ? ToString(encodedURI).
Let reservedURISet be a String containing one instance of each code unit valid in uriReserved plus "#".
Return ? Decode(uriString, reservedURISet).

Note

The code point # is not decoded from escape sequences even though it is not a reserved URI code point.

19.2.6.3 decodeURIComponent ( `encodedURIComponent` )

The decodeURIComponent function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by the encodeURIComponent function is replaced with the UTF-16 encoding of the code points that it represents.

The decodeURIComponent function is the %decodeURIComponent% intrinsic object. When the decodeURIComponent function is called with one argument encodedURIComponent, the following steps are taken:

Let componentString be ? ToString(encodedURIComponent).
Let reservedURIComponentSet be the empty String.
Return ? Decode(componentString, reservedURIComponentSet).

19.2.6.4 encodeURI ( `uri` )

The encodeURI function computes a new version of a UTF-16 encoded (6.1.4) URI in which each instance of certain code points is replaced by one, two, three, or four escape sequences representing the UTF-8 encoding of the code points.

The encodeURI function is the %encodeURI% intrinsic object. When the encodeURI function is called with one argument uri, the following steps are taken:

Let uriString be ? ToString(uri).
Let unescapedURISet be a String containing one instance of each code unit valid in uriReserved and uriUnescaped plus "#".
Return ? Encode(uriString, unescapedURISet).

Note

The code point # is not encoded to an escape sequence even though it is not a reserved or unescaped URI code point.

19.2.6.5 encodeURIComponent ( `uriComponent` )

The encodeURIComponent function computes a new version of a UTF-16 encoded (6.1.4) URI in which each instance of certain code points is replaced by one, two, three, or four escape sequences representing the UTF-8 encoding of the code point.

The encodeURIComponent function is the %encodeURIComponent% intrinsic object. When the encodeURIComponent function is called with one argument uriComponent, the following steps are taken:

Let componentString be ? ToString(uriComponent).
Let unescapedURIComponentSet be a String containing one instance of each code unit valid in uriUnescaped.
Return ? Encode(componentString, unescapedURIComponentSet).