Stage 3 Draft / June 19, 2018

String.prototype.trimStart/trimEnd (plus trimLeft/trimRight)

1String.prototype.trim ( )

The following steps are taken:

  1. Let O be ? RequireObjectCoercible(this value).
  2. Let S be ? ToString(O).
  3. Let T be a String value that is a copy of S with both leading and trailing white space removed. The definition of white space is the union of WhiteSpace and LineTerminator. When determining whether a Unicode code point is in Unicode general category “Space_Separator” (“Zs”), code unit sequences are interpreted as UTF-16 encoded code point sequences as specified in 6.1.4.
  4. Return T.
  1. Let S be this value.
  2. Return ? TrimString(S, "start+end").
Note

The trim function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.

2String.prototype.trimStart ( )

The following steps are taken:

  1. Let S be this value.
  2. Return ? TrimString(S, "start").
Note

The trimStart function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.

3String.prototype.trimEnd ( )

The following steps are taken:

  1. Let S be this value.
  2. Return ? TrimString(S, "end").
Note

The trimEnd function is intentionally generic; it does not require that its this value be a String object. Therefore, it can be transferred to other kinds of objects for use as a method.

4Runtime Semantics: TrimString ( string, where )

The abstract operation TrimString is called with arguments string and where, and interprets the String value string as a sequence of UTF-16 encoded code points, as described in 6.1.4. It performs the following steps:

  1. Let str be ? RequireObjectCoercible(string).
  2. Let S be ? ToString(str).
  3. If where is "start", let T be a String value that is a copy of S with leading white space removed.
  4. Else if where is "end", let T be a String value that is a copy of S with trailing white space removed.
  5. Else,
    1. Assert: where is "start+end".
    2. Let T be a String value that is a copy of S with both leading and trailing white space removed.
  6. Return T.

The definition of white space is the union of WhiteSpace and LineTerminator. When determining whether a Unicode code point is in Unicode general category “Zs”, code unit sequences are interpreted as UTF-16 encoded code point sequences as specified in 6.1.4.

AAdditional ECMAScript Features for Web Browsers

A.1String.prototype.trimLeft ( )

Note

The property trimStart is preferred. The trimLeft property is provided principally for compatibility with old code. It is recommended that the trimStart property be used in new ECMAScript code.

The initial value of the trimLeft property is the same function object as the initial value of the String.prototype.trimStart property.

A.2String.prototype.trimRight ( )

Note

The property trimEnd is preferred. The trimRight property is provided principally for compatibility with old code. It is recommended that the trimEnd property be used in new ECMAScript code.

The initial value of the trimRight property is the same function object as the initial value of the String.prototype.trimEnd property.

BCopyright & Software License

Copyright Notice

© 2018 Sebastian Markbåge, Tom Schuster

Software License

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