substr vs substring vs slice

These three methods differ in the parameters, but results in the same primitive string. You can stick to one at all times, or pick the best suited one for each use case.

When passing in a negative value as first parameter they handle it differently:

substr

Some older interpreters (IE8) will treat a negative start index as 0.

substring

The smallest value will be used as start index. A negative start index will be treated as 0.

slice

A negative start index is acceptable, and will start counting from the end.

Performance stats at jsperf.com

The constructors

String.substr(begin, [length])

Starts from begin position and reads length amonut of characters where stop can not be a negative value.

String.substring(start, [stop])

Starts from start position and stops at stop position where stop can not be a negative value.

String.slice(begin, [end])

Starts from begin position and ends at end position where end can be a negative value counting from the end.

Some examples that produce the same result, but have a different set of parameters in the call.

Run
var str = 'Hello World';

console.log(str.substr(1));          // ello World
console.log(str.substring(1));       // ello World
console.log(str.slice(1));           // ello World

console.log(str.substr(-1));         // d
console.log(str.substring(10));      // d
console.log(str.slice(-1));          // d

console.log(str.substr(1, 9));       // ello Worl
console.log(str.substring(1, 10));   // ello Worl
console.log(str.slice(1, -1));       // ello Worl

console.log(str.substr(-4, 3));      // orl
console.log(str.substring(7, 10));   // orl
console.log(str.slice(-4, -1));      // orl

console.log(str.substr(0, 1));       // H
console.log(str.substring(0, 1));    // H
console.log(str.slice(0, 1));        // H

Be aware, all of these can run into issues with multibyte characters.

Run
var str = 'हिं';

console.log(str);                  // हिं
console.log(str.length);           // 3

console.log(str.substr(0, 1));     // ह
console.log(str.substring(0, 1));  // ह
console.log(str.slice(0, 1));      // ह

console.log(str.substr(-2, 1));    // ि
console.log(str.substr(1, 1));     // ि
console.log(str.substring(1, 2));  // ि
console.log(str.slice(-2, 2));     // ि
console.log(str.slice(1, 2));      // ि

console.log(str.substr(-1));       // ं
console.log(str.substr(2));        // ं
console.log(str.substring(2));     // ं
console.log(str.slice(-1));        // ं
console.log(str.slice(2));         // ं

$str = 'Hello World';
$result = substr($str, 3, 2);     // lo
$result = substr($str, 1, -2);    // ello Wor
$result = substr($str, -5, -2);   // Wor

Run
var str = 'Hello World';
console.log(str.substr(3, 2));    // lo
console.log(str.slice(1, -2));    // ello Wor
console.log(str.slice(-5, -2));   // Wor