How to check if an object has a function? (DoJo)

Question

var testObj = this.getView();

How can I check with DoJo (or just native JS) if testObj has callableFunction before I actually try to call callableFunction() and fail if it isn't there? I would prefer a native-DoJo solution as I need this to work on all browsers.

score 98 · Accepted Answer · answered Feb 19 '13 at 16:06

98

You can call it like this:

testObj.callableFunction && testObj.callableFunction();

or in details:

if (typeof testObj.callableFunction == 'function') {
    testObj.callableFunction();
}

answered Feb 19 '13 at 16:06

dfsq

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@Ethan In the his case it's safe to use == since typeof operator always returns string type. But if you use === in the project then for consistency sake — yes. – dfsq Nov 30 '15 at 04:43
@dfsq Thanks for clarifying. So, if we need to check for non existence, we can comfortably do == "undefined". – Ethan Nov 30 '15 at 10:59

score 4 · Answer 2 · answered Feb 19 '13 at 16:32

4

dojo has a function that you can use to perform the test.

require(["dojo/_base/lang"], function(lang){

  var testObj = this.getView();
  if(lang.isFunction(testObj.callableFunction)){
    testObj.callableFunction();
  }

});

answered Feb 19 '13 at 16:32

Craig Swing

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score 3 · Answer 3 · answered Feb 19 '13 at 16:09

3

You should test that the property exists and is a function:

var returnFromCallable = typeof testObj.callableFunction === 'function' &&
    testObj.callableFunction();

answered Feb 19 '13 at 16:09

jbabey

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How to check if an object has a function? (DoJo)

3 Answers3