Since you seem to be interested in performance, I profiled these with firebug. Here are the results I got:

str.replace( / +/g, ' ' )  -> 790ms str.replace( / +/g, ' ' )  -> 380ms str.replace( / {2,}/g, ' ' ) -> 470ms str.replace( /\s\s+/g, ' ' ) -> 390ms str.replace( / +(?= )/g, ' ') -> 3250ms 

This is on Firefox, running 100k string replacements.

I encourage you to do your own profiling tests with firebug, if you think performance is an issue. Humans are notoriously bad at predicting where the bottlenecks in their programs lie.

(Also, note that IE 8's developer toolbar also has a profiler built in -- it might be worth checking what the performance is like in IE.)

Since you seem to be interested in performance, I profiled these with firebug. Here are the results I got:

str.replace( /  +/g, ' ' ) -> 380ms str.replace( /\s\s+/g, ' ' ) -> 390ms str.replace( / {2,}/g, ' ' ) -> 470ms str.replace( / +/g, ' ' )  -> 790ms str.replace( / +(?= )/g, ' ') -> 3250ms 

This is on Firefox, running 100k string replacements.

I encourage you to do your own profiling tests with firebug, if you think performance is an issue. Humans are notoriously bad at predicting where the bottlenecks in their programs lie.

(Also, note that IE 8's developer toolbar also has a profiler built in -- it might be worth checking what the performance is like in IE.)

Since you seem to be interested in performance, I profiled these with firebug. Here are the results I got:

str.replace( / +/g, ' ' ) -> 795ms str.replace( / +/g, ' ' ) -> 379ms str.replace( / {2,}/g, ' ' ) -> 467ms str.replace( /\s\s+/g, ' ' ) -> 391ms 

This is on Firefox, running 100k string replacements.

I encourage you to do your own profiling tests with firebug, if you think performance is an issue. Humans are notoriously bad at predicting where the bottlenecks in their programs lie.

(Also, note that IE 8's developer toolbar also has a profiler built in -- it might be worth checking what the performance is like in IE.)

Since you seem to be interested in performance, I profiled these with firebug. Here are the results I got:

str.replace( / +/g, ' ' )  ->  790ms str.replace( / +/g, ' ' )  ->  380ms str.replace( / {2,}/g, ' ' )  ->  470ms str.replace( /\s\s+/g, ' ' )  ->  390ms str.replace( / +(?= )/g, ' ') -> 3250ms 

This is on Firefox, running 100k string replacements.

I encourage you to do your own profiling tests with firebug, if you think performance is an issue. Humans are notoriously bad at predicting where the bottlenecks in their programs lie.

(Also, note that IE 8's developer toolbar also has a profiler built in -- it might be worth checking what the performance is like in IE.)