Question

We know that by default, the ‘obj’ below is string. Without using ‘parseInt’, how does JavaScript compare it with a number?

obj = document.frm.weight.value;
if( obj < 0 || obj > 5 ){
    alert("Enter valid range!");
    return false;
}

Answer 1

If one of the operands of < or > is number, the other one will be casted to a number.

alert("3" > 3);   // false
alert("3.5" > 3); // true

EDIT and further explanation:

If it is not possible to cast the other parameter into a number, it is casted into the special value called NaN – the abbreviation stands for “Not a Number”. The NaN value has a special property that it is absolutely incomparable – all relation operators like <, > and = will return false if one of the arguments is NaN.

alert("" > 3);      // false
alert("3.5?" > 3);  // false
alert({} > 3);      // false

Also, note that in the second line, if we used

alert(parseInt("3.5?") > 3);

it would alert true, because parseInt reads "3.5" from the string "3.5?", then stops reading at "?" and thus evaluates to 3.5. However,

alert("3.5?" > 3);

returns false because the cast from string to number is not as benevolent as parseInt. As "3.5" indeed isn’t a number, it is casted to NaN.