How will ' - '(minus) will work in Javascript when used b/w two strings?

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<script language="javascript" type="text/javascript">
var num1="5";
var num2="3";
var sum=num1-num2;
document.write("The sum is:" +sum);
</script>

Addition will give 53 as O/p alright.
subtraction is giving 2 as o/p.Why this o/p is produced.
Want know the reason for that.

Posted 16-Oct-14 19:50pm

Janardhanam Julapalli

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OriginalGriff · Accepted Answer · 2014-10-16T20:04:00

Javascript is a weakly typed language, which means it tries to convert data for you when it can.
And it specifically has a string concatenation operator: '+'

So when it parses your code and sees this:

JavaScript

var num1="5";
var num2="3";
var sum=num1+num2;

It looks at the actual datatypes you have given it and because at least one of them is a string it decides to use the string concatenation operator and combines the strings - so you get a string result "53"

But...there is nothing sensible that can be subtracted from strings - so there is no "string deconcatenation" operator. So when it encounters this:

JavaScript

var num1="5";
var num2="3";
var sum=num1-num2;

it has to use the subtract operator, and converts each strign to a number first - so you get 5 - 3, or 2