Javascript error object is not a function: why the code needs window.?

Question

I am having trouble understanding the difference between

var maxResult = window.max(maxValInt1, maxValInt2);

that works well, and

var maxResult = max(maxValInt1, maxValInt2);

that gets a error "object is not a function".

Why do I need to add window. before the max function?

I'm new in Java Script and it's helpful if you can explain with detail.

<div id="maxOfTwo">Max function: <input type = "number" name="val1" value="0">, <input type = "number" name="val2" value="0"> = <span></span></div>

<script type="text/javascript">

function max(val1, val2){
    if(val1 > val2){
        return val1;
    }else{
        return val2;
    }
}

window.onload = function() {
    var max = document.getElementById("maxOfTwo");
    var maxNumber1 = max.children[0];
    var maxNumber2 = max.children[1];
    maxNumber1.addEventListener("blur", doMax);
    maxNumber2.addEventListener("blur", doMax);
    function doMax() {
        var maxValue1 = maxNumber1.value;
        var maxValue2 = maxNumber2.value;
        var maxValInt1 = parseInt(maxValue1);
        var maxValInt2 = parseInt(maxValue2);
        var maxResult = window.max(maxValInt1, maxValInt2);
        max.children[2].innerHTML = maxResult;
    }
}
</script>

Quentin · Accepted Answer · 2015-01-04 00:24:21Z

2

var max = document.getElementById("maxOfTwo");

You have a locally scoped variable with the same name.

If you don't explicitly access the property of the window object, then the scope chain will find your HTML Element Object first.

answered Jan 4, 2015 at 0:24

Quentin

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