A comparison of substring methods.
June 25, 2011
// 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 reversable, as it will always use it's 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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