How to get array keys in Javascript?

javascript arrays key
DisgruntledGoat picture DisgruntledGoat · Mar 24, 2010 · Viewed 324.7k times · Source

I have an array created with this code:

var widthRange = new Array();
widthRange[46] = { min:0,  max:52 };
widthRange[66] = { min:52, max:70 };
widthRange[90] = { min:70, max:94 };

I want to get each of the values 46, 66, 90 in a loop. I tried for (var key in widthRange) but this gives me a whole bunch of extra properties (I assume they are functions on the object). I can't use a regular for loop since the values are not sequential.

Answer

SLaks picture SLaks · Mar 24, 2010

You need to call the hasOwnProperty function to check whether the property is actually defined on the object itself (as opposed to its prototype), like this:

for (var key in widthRange) {
    if (key === 'length' || !widthRange.hasOwnProperty(key)) continue;
    var value = widthRange[key];
}

Note that you need a separate check for length.
However, you shouldn't be using an array here at all; you should use a regular object. All Javascript objects function as associative arrays.

For example:

var widthRange = { };  //Or new Object()
widthRange[46] = { sel:46, min:0,  max:52 };
widthRange[66] = { sel:66, min:52, max:70 };
widthRange[90] = { sel:90, min:70, max:94 };

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