Question

Got a query from a collegue. I am not able to answer this question.

var x = '9'; // Line no 1
x=='7' // Line no 2
//doing something with x

Line no 2 is not giving any error.

another scenario

var x == '7';

Browser :
SyntaxError: missing ; before statement

This is because the assignment is always done by single ‘=’.

Question :

1. How first scenario executes?

Answer 1

x == '7'

This line is a boolean expression. Its value is calculated and simply discarded. It is encouraged by some people to use yoda-conditions

if(7 == x)

instead of

if(x == 7)

So that you don’t accidentally type if(x = 7) and get yourself a hard to find bug.

This

var x == '7'

on the other hand, is supposed to be a variable declaration, so the == operator is illegal here.