what is an illegal invocation typeerror in javascript

Question

I have javascript code that raises an alert if it's being run in the browser, but which I don't want to raise alerts when I run unit tests.

I tried to solve this by having a line

if( allowAlerts === false ){
    alert = console.log;
}

but when I then run

alert("This bad thing happened");

I get back

TypeError: Illegal invocation

directly reassigning alert was a kludgey solution, and I can easily solve the problem in other ways, but I've never come across an illegal invocation error before and was hoping someone could explain what it means.

score 9 · Accepted Answer · answered Oct 18 '13 at 16:56

9

The console.log function needs its calling context to be the console.

Use

alert = console.log.bind(console);

Or if you want to be compatible with old IE :

alert = function(){ console.log.apply(console, arguments) };

answered Oct 18 '13 at 16:56

Denys Séguret

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Or just shim `bind` :) – Adam Rackis Oct 18 '13 at 17:13
@AdamRackis As you can't make a complete shim of bind, I'm vary of this solution. Either I don't care for old browsers, or I avoid `shim` completely. – Denys Séguret Oct 18 '13 at 17:22
How do you mean? Are you mixing up the bind shim with Object.create?? Doesn't the bind shim simulate setting `this` and curry parameters as the real thing does? – Adam Rackis Oct 18 '13 at 17:49
@AdamRackis Look at bind at the MDN, it lists the limits of what a shim can do. – Denys Séguret Oct 18 '13 at 22:06

what is an illegal invocation typeerror in javascript

1 Answers1