Use the typeof algorithm

Typeof has an undefined operand and returns “undefined”.

Here, x is defined as the operand:

There are five cases;

Typeof (x) returns “number”;

Typeof (x) returns “string”;

Typeof (x) returns a Boolean;

Object, array, null&sponge; When: typeof(x) returns “object”;

The function typeof(x) returns “function”.

Such as:

<script type="text/javascript">
　　　　var x=123456;
　　　　alert( typeof(x));//The pop-up "number".
</script>