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#3857 — Add String.prototype[@@toStringTag] and other pre-ES6 constructors' toStringTag property

• bug_id: 3857
• creation_ts: 2015-02-12 22:53:00 -0800
• short_desc: Add String.prototype[@@toStringTag] and other pre-ES6 constructors' toStringTag property
• delta_ts: 2015-02-15 14:56:01 -0800
• product: Draft for 6th Edition
• component: technical issue
• version: Rev 33: February 12, 2015 Draft
• rep_platform: All
• op_sys: All
• bug_status: RESOLVED
• resolution: WONTFIX
• priority: Normal
• bug_severity: normal
• everconfirmed: true
• reporter: Gary Guo
• assigned_to: Allen Wirfs-Brock
• cc: nbdd0121

---

• commentid: 12509
• comment_count: 0
• who: Gary Guo
• bug_when: 2015-02-12 22:53:06 -0800

By letting
Array.prototype[@@toStringTag] = 'Array',
String.prototype[@@toStringTag] = 'String',
Function.prototype[@@toStringTag] = 'Function',
Error.prototype[@@toStringTag] = 'Error',
Boolean.prototype[@@toStringTag] = 'Boolean',
Number.prototype[@@toStringTag] = 'Number',
Date.prototype[@@toStringTag] = 'Date',
RegExp.prototype[@@toStringTag] = 'RegExp,
we are able to simplify Object.prototype.toString's algorithm and make constructor.prototype[@@toStringTag] more consistent.

What's more, it can also preserve compatibility for pre-ES6 codes, since most prototypes are now ordinary objects.
In ES5:
Object.prototype.toString.call(String.prototype) == '[object String]'
In current ES6 spec:
Object.prototype.toString.call(String.prototype) == '[object Object]'
After my proposal:
Object.prototype.toString.call(String.prototype) == '[object String]'

---

• commentid: 12742
• comment_count: 1
• who: Allen Wirfs-Brock
• bug_when: 2015-02-15 14:56:01 -0800

the final design for Object.prototype.toString was settled at the Jany 2015 TC39 meeting https://github.com/tc39/tc39-notes/blob/master/es6/2015-01/jan-28.md#45-tostringtag