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A for In loop in JavaScript is typically used to traverse an array
The first thing to understand is what an array is, an array, which is actually a collection of a set of similar variables. Let's take a look at an array instance that holds a hobby:
<body>
<script type= "Text/javascript" >
var x;
var hobbies = new Array ();
Hobbies[0] = "JavaScript";
HOBBIES[1] = "CSS";
HOBBIES[2] = "basketball";
for (x in Hobbies)//each variable in the array
{
document.write (Hobbies[x] + "<br/>");
}
</script>
</body>
The output results are as follows:
Javascript
Css
Basketball
Let's analyze the above example:
The var hobbies = new Array ();
Hobbies[0] = "JavaScript"; and the next two sentences are assigned to the hobbies array. This is not the same as the variables we've seen before, hobbies a "[0]", which is the index of the variable. As we've already said, arrays are sets of variables, so we need to specify which variable in the array to assign to before assigning a value. Here, "[0]" means the first variable contained in the hobbies array, and yes, the index of the array is starting at 0, which may be a bit awkward at first, and slowly get used to it.
The last for In loop is well understood,
for (x in Hobbies)//each variable in the array
{
document.write (Hobbies[x] + "<br/>");
}
Represents all the variables that traverse the hobbies array and outputs them individually.
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