Comparisons in JavaScript

 

• Greater/less than: a > b, a < b.
• Greater/less than or equals: a >= b, a <= b.
• Equals: a == b, please note the double equality sign == means the equality test, while a single one a = b means an assignment.
• Not equals. In JavaScript it’s written as a != b.

In this article we’ll learn more about different types of comparisons, how JavaScript makes them, including important peculiarities.

At the end you’ll find a good recipe to avoid “JavaScript quirks”-related issues.

Boolean is the result

All comparison operators return a Boolean value:

• true – means “yes”, “correct” or “the truth”.
• false – means “no”, “wrong” or “not the truth”.

For example:

alert( 2 > 1 );  // true (correct)

alert( 2 == 1 ); // false (wrong)

alert( 2 != 1 ); // true (correct)

A comparison result can be assigned to a variable, just like any value:

let result = 5 > 4; // assign the result of the comparison

alert( result ); // true

String comparison

To see whether a string is greater than another, JavaScript uses the so-called “dictionary” or “lexicographical” order.

In other words, strings are compared letter-by-letter.

For example:

alert( 'Z' > 'A' ); // true

alert( 'Glow' > 'Glee' ); // true

alert( 'Bee' > 'Be' ); // true

The algorithm to compare two strings is simple:

1. Compare the first character of both strings.
2. If the first character from the first string is greater (or less) than the other string’s, then the first string is greater (or less) than the second.
3. Otherwise, if both strings’ first characters are the same, compare the second characters the same way.
4. Repeat until the end of either string.
5. If both strings end at the same length, then they are equal. Otherwise, the longer string is greater.

In the first example above, the comparison 'Z' > 'A' gets to a result at the first step.

The second comparison 'Glow' and 'Glee' needs more steps as strings are compared character-by-character:

• G is the same as G.
• l is the same as l.
• o is greater than e. Stop here. The first string is greater.