Call a Javascript function stored in an object property [duplicate]

Question

How come the code below doesn't work?

var x = {};
x.a = alert;
x.a('asdf'); // TypeError: Illegal invocation

The alert function needs is calling context to be window so it can't be called with a different context — adeneo
– adeneo, Commented Feb 24, 2015 at 10:52
Agree on the duplication but I believe my example is clearer, as is the answer easier to read and understand. (I "knew" this q was posted but didn't find it) — LosManos
– LosManos, Commented Feb 24, 2015 at 11:11

Quentin · Accepted Answer · 2015-02-24 10:51:44Z

2

Because the internals of the alert function requires that the value of this be window.

x.a.call(window,'asdf');

… will work.

answered Feb 24, 2015 at 10:51

Quentin

949k136 gold badges1.3k silver badges1.4k bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

It looks like window can be replaced with null too(!)

Can you explain it more.

x.a.call(null, 'asdf'); works.