Comparison Operators

Javascript has the following comparison operators:

  • < less than
  • <= less than or equal
  • > greater than
  • >= greater than or equal

Use these to compare numbers with numbers or strings with strings.

Strings are compared lexicographically:

console.log("Hello" < "Goodbye");
console.log("Hello" < "Hi");

There are no "strict" versions of comparison operations. So, if you mix types, JavaScript will go about converting types!

console.log("42" < 5);    // "42" is converted to the number 42
console.log("" < 5);      // "" is converted to the number 0
console.log("Hello" < 5); // "Hello" is converted to NaN
console.log([2] < 5);     // [2] is converted to the number 2
console.log([1, 2] < 5);  // [1, 2] is converted to "1,2"
console.log(true > 2);    // true is converted to the number 1

More madness:

console.log(NaN < 1);
console.log(NaN > 1);
console.log(undefined < 1); 
console.log(undefined > 1);     
console.log(null < 1);
console.log(null > 1);

The logic(!) behind the madness:

  • When one operand is a string, and the other is a number, the string is converted to a number before comparison.
  • When the string is non-numeric, numeric conversion returns NaN. Comparing with NaN always returns false.
    • However, null, false, and empty string convert to 0. And, true converts to the number 1.
  • When one operand is an object, and the other is a number, the object is converted to a number before comparison.

Avoid mixed-type comparisons!