Filtering out numeric indexes from an array with javascript

Question

This is the code i have written to filter out Numeric values from an array, but it is returning the complete array. I am not able to find out the problem in my code. Please help me i am stuck...

<!doctype html>
<html lang="en">
    <head>
  <meta charset="utf-8">
  <title>html demo</title>
</head>
<body>
<script>
    arr = ["apple", 5, "Mango", 6];
    function filterNumeric(arrayName){
        var i = 0;
        var numericArray=[];
        for (i; i <arrayName.length;i++){
            if (typeof(arrayName[i] === 'number')) {
                numericArray+=arrayName[i];
            }
        }
        return numericArray;
    }

    var filter = filterNumeric(arr);
    alert(filter);
</script>

</body>
</html>

Scimonster · Accepted Answer · 2014-09-16 09:24:22Z

1

Typo in the typeof check:

if (typeof(arrayName[i]) === 'number') {
//                    ^^^ close the parentheses here
//                                 ^^^ not there

answered Sep 16, 2014 at 9:24

Scimonster

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Jean-Karim Bockstael · Accepted Answer · 2014-09-16 09:33:48Z

JavaScript arrays have a built-in filtering method:

var arr = ["apple", 5, "Mango", 6];
var filtered = arr.filter(function(item) { return (typeof item === "number")});
console.log(filtered); // Array [5,6]

As for your original code, beware that typeof is an operator, not a function, so

if (typeof(foo === "whatever")) {
    // ...
}

is equivalent to

if (typeof some_boolean_value) {
    // ...
}

which evaluates to

if ("boolean") {
    // ...
}

which will always be true, this is why you ended up with the whole content with no filtering whatsoever.

Also note that the += operator is not overloaded for arrays, you will end up with a string concatenation of the remaining values:

var foo = [];
var bar = [1,2,3,4];
foo += bar[2];
console.log(foo); // "3"
console.log(typeof foo); // "string"

you must use the push method instead:

var foo = [];
var bar = [1,2,3,4];
foo.push(bar[2]);
console.log(foo); // Array [3]
console.log(typeof foo); // "object"

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