Can someone clarify if there is a distinction between using x.f.call(x, ...) and x.f(...) in JavaScript?

Reviewing some code reveals the following:

this.f.call(this);

Or in other scenarios:

this.someObj.f.call(this.someObj);

Is there a distinction between these and:

this.f();
this.someObj.f();

Under what circumstances might the behavior differ? (e.g. if 'this' or 'someObj' is null, not an object, or 'f' is not actually a function? It's hard to determine if one would trigger an exception while the other wouldn't, unless I'm overlooking something...)

EDIT: Clarification - I understand that '.call' can be used to define the 'this' value accessed by the function. It comes in handy when using 'obj.f()' syntax isn't feasible (due to 'f' not being a property of 'obj' or uncertainty about it). My query doesn't delve into the workings of '.call' in general, but rather focuses on this specific case where the rationale behind employing '.call' over the object-property syntax eludes me.

javascript

Answer №1

There is zero distinction between the two choices.

If we refer to the language specification for regular function calls and also take a look at Function.prototype.call, it becomes apparent that they perform identically.

In particular,

x.f.call(x) accomplishes this:

It returns the result of invoking the [[Call]] internal method of func, using thisArg as the value for 'this' and argList as the arguments list.

Whereas a regular call does:

It returns the result of invoking the [[Call]] internal method on func, using thisValue as the 'this' value and providing the argument values in the argList.

With respect to how `this` is resolved (specified in 11.2.3 7.b.i in the spec).

All modern JavaScript implementations (yes, even IE8 modern) adhere to this standard.

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