JavaScript: Slice, Substring, or Substr?

A comparison of substring methods.

In JavaScript, substrings are primarily extracted through one of following String methods: slice, substring, substr.

// slice 
// syntax: string.slice(start [, stop])
"Good news, everyone!".slice(5,9); 
// 'news'

// substring 
// syntax: string.substring(start [, stop])
"Good news, everyone!".substring(5,9); 
// 'news'

// substr
// syntax: string.substr(start [, length])
"Good news, everyone!".substr(5,4); 
// 'news'

All three of these methods take in a start index and an optional stop index (or length) parameter, but they differ in some important ways:

  • substr can give inconsistent results. Modern browers allow using a negative start index to indicate the number of characters from the end of the string, but IE8 and lower treat a negative start index as 0.
  • substring's parameters are reversible, as it will always use its smallest parameter value as the start index and largest value as the stop index. substring will treat a negative start index as 0.
  • slice extracts from the end of the string if the starting index is negative.

Negative start index

"Good news, everyone!".substring(-4);
// "Good news, everyone!"

"Good news, everyone!".substr(-4);
// "one!" modern browsers, including IE9
// "Good news, everyone!" IE8 and lower

"Good news, everyone!".slice(-4); 
// "one!"

Since all three methods have roughly equivalent performance, my preference is to use slice. It supports extracting from the end of the string and I feel that returning an empty string when start index > stop follows the principle of least surprise better than substring's swapping of parameters. I avoid substr because of the browser inconsistency.


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