How “100″ != 100

We’re all probably used to the usual comparison methods in different languages. After all, if you learned some sort of Math, you know == is a rather common comparison operator in some programming languages. Javascript has it too, but some of the comparisons done in Javascript sometimes produces rather ambiguous results. Don’t believe me? Fire up your Firebug console and try the expressions in the first table below.

So, what happened in the last case? The string 5 is definitely not the same as the integer 5. But, apparently some conversion happens under the hood while comparing.

If the two operands are not of the same type, JavaScript converts the operands then applies strict comparison. If either operand is a number or a boolean, the operands are converted to numbers; if either operand is a string, the other one is converted to a string
Mozilla Developer Center

In cases like this, especially in Javascript since it’s a loosely typed language, it is better to use the strict comparison operator. In case you’re wondering what a strict comparison operator, instead of using “==” and “!=”, you will use “===” and “!==” respectively. By using the strict comparison operator, Javascript does not perform any conversion and compares both the operands values and types.

Now, here’s the same expressions as above using the strict equality operator and check out the different results in some cases.