Compare Strings in JavaScript
What does it mean for two strings to be equal, or for one string to be greater than the other in JavaScript?
JavaScript's triple equals operator === returns
true if two strings are exactly equal, and false otherwise:
'hello' === 'hello'; // true
'Hello' === 'hello'; // falseThe < and > operators compare strings in lexicographical order. Lexicographical order essentially means "dictionary order".
In simpler terms, a < b if the first character of a
comes before the first character of b in the ASCII table,
or if the first characters of a and b are equal and a.slice(1) < b.slice(1).
'alpha' < 'zeta'; // true, because 'a' comes before 'z'
'alpha' < 'Zeta'; // false, because 'Z' = 90 in ASCII, and 'a' = 97
'one' < '1'; // false, because '1' = 49 in ASCII, and 'o' = 111
'octo' < 'okto'; // true, because 'c' = 99, and 'k' = 107
'a' < 'alpha'; // true, because end of string = '0' in ASCIISorting an Array of Strings
JavaScript's Array#sort() function sorts by lexicographic order automatically.
['Zeta', '1', 'alpha', ''].sort(); // ['', '1', 'Zeta', 'alpha']Lodash's sortBy() function also sorts by lexicographic
order automatically, as long as you're sorting an array of strings.
_.sortBy(['Zeta', '1', 'alpha', '']); // ['', '1', 'Zeta', 'alpha']What about sorting an array of objects
based on a string property? The Array#sort() function takes a callback
parameter that takes 2 values a and b, and should return:
0ifaandbare equal- A positive number if
a > b - A negative number if
a < b
Given an array of objects with a lastName property, below is one way
to sort the array by lastName.
const characters = [
{ firstName: 'Jean-Luc', lastName: 'Picard', rank: 'Captain', age: 59 },
{ firstName: 'Will', lastName: 'Riker', rank: 'Commander', age: 29 },
{ firstName: 'Geordi', lastName: 'La Forge', rank: 'Lieutenant', age: 29 }
];
characters.sort((a, b) => {
if (a === b) {
return 0;
}
return a.lastName < b.lastName ? -1 : 1;
});
// La Forge, Picard, Riker
characters;A more concise alternative is using JavaScript's built-in localeCompare() function. Calling a.localeCompare(b) returns -1 if a < b,
0 if a === b, and 1 if a > b.
const characters = [
{ firstName: 'Jean-Luc', lastName: 'Picard', rank: 'Captain', age: 59 },
{ firstName: 'Will', lastName: 'Riker', rank: 'Commander', age: 29 },
{ firstName: 'Geordi', lastName: 'La Forge', rank: 'Lieutenant', age: 29 }
];
characters.sort((a, b) => a.lastName.localeCompare(b.lastName));
// La Forge, Picard, Riker
characters;