Why is delete not allowed in Javascript5 strict mode?

javascript ecmascript-5 strict-mode
sircodesalot picture sircodesalot · May 20, 2013 · Viewed 39.1k times · Source

I'm fairly new to javascript. I noticed that apparently when operating in "use strict" mode, you can't delete objects. I'm not a huge fan of deleting things (since, in theory, scope should take care of that anyway), but I wonder what was the motivation behind removing this feature?

Answer

Pointy picture Pointy · May 20, 2013

The delete statement is still allowed in strict mode, but some particular uses of it are erroneous. It's only allowed for object properties, not simple names, and only for object properties that can be deleted.

Thus

var a = {x: 0};
delete a.x;

is fine, but

delete Object.prototype;

is not, and neither is

delete a;

(The latter is actually a syntax-level error, while an attempt to delete an undeletable property is a runtime error.)

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