Detecting an undefined object property

Question

What\'s the best way of checking if an object property in JavaScript is undefined?

Answer 1

From lodash.js.

var undefined;
function isUndefined(value) {
  return value === undefined;
}

It creates a local variable named undefined which is initialized with the default value -- the real undefined, then compares value with the variable undefined.

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Update 9/9/2019

I found Lodash updated its implementation. See my issue and the code.

To be bullet-proof, simply use:

function isUndefined(value) {
  return value === void 0;
}