javascript - Why does ES6 define map.length==0? - Stack Overflow

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According to MDN:

Map.length

The value of the length property is 0.

What is the use case for this? I understand why Map.size is semantically correct. But surely a Map.length that almost always returns the "wrong" answer is a bad idea, especially if there's an oversight migrating code from ES5. Is there a way to force an error when this is used?

According to MDN:

Map.length

The value of the length property is 0.

What is the use case for this? I understand why Map.size is semantically correct. But surely a Map.length that almost always returns the "wrong" answer is a bad idea, especially if there's an oversight migrating code from ES5. Is there a way to force an error when this is used?

• javascript
• ecmascript-6

Share Improve this question Follow asked Oct 5, 2015 at 18:52 jimm101jimm101 99811 gold badge1515 silver badges3737 bronze badges 3

• Here's the relevant part of the spec, too – James Thorpe Commented Oct 5, 2015 at 18:54
• 6 It says Map.length is 0. Not that the .length property of a new Map() is 0. Try: var m = new Map(); console.log(m.length, m.size, Map.length);. – gen_Eric Commented Oct 5, 2015 at 18:55
• 1 Still doesn't explain why Map.length === 0 though. – Alexander O'Mara Commented Oct 5, 2015 at 18:57

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Sorted by: Reset to default 15

Constructors in JavaScript are regular functions, and the length property of a function corresponds to the number of formal parameters expected by the function, which is 0 in the case of Map.

Contrast this with RegExp.length, which is 2, because the RegExp constructor expects two parameters (pattern and flags).

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