You can access capturing groups like this:
var myString = "something format_abc";
var myRegexp = /(?:^|\s)format_(.*?)(?:\s|$)/g;
var myRegexp = new RegExp("(?:^|\s)format_(.*?)(?:\s|$)", "g");
var match = myRegexp.exec(myString);
console.log(match[1]); // abc
And if there are multiple matches you can iterate over them:
var myString = "something format_abc";
var myRegexp = new RegExp("(?:^|\s)format_(.*?)(?:\s|$)", "g");
match = myRegexp.exec(myString);
while (match != null) {
// matched text: match[0]
// match start: match.index
// capturing group n: match[n]
console.log(match[0])
match = myRegexp.exec(myString);
}
Edit: 2019-09-10
As you can see the way to iterate over multiple matches was not very intuitive. This lead to the proposal of the String.prototype.matchAll
method. This new method is expected to ship in the ECMAScript 2020 specification. It gives us a clean API and solves multiple problems. It has been started to land on major browsers and JS engines as Chrome 73+ / Node 12+ and Firefox 67+.
The method returns an iterator and is used as follows:
const string = "something format_abc";
const regexp = /(?:^|\s)format_(.*?)(?:\s|$)/g;
const matches = string.matchAll(regexp);
for (const match of matches) {
console.log(match);
console.log(match.index)
}
As it returns an iterator, we can say it's lazy, this is useful when handling particularly large numbers of capturing groups, or very large strings. But if you need, the result can be easily transformed into an Array by using the spread syntax or the Array.from
method:
function getFirstGroup(regexp, str) {
const array = [...str.matchAll(regexp)];
return array.map(m => m[1]);
}
// or:
function getFirstGroup(regexp, str) {
return Array.from(str.matchAll(regexp), m => m[1]);
}
In the meantime, while this proposal gets more wide support, you can use the official shim package.
Also, the internal workings of the method are simple. An equivalent implementation using a generator function would be as follows:
function* matchAll(str, regexp) {
const flags = regexp.global ? regexp.flags : regexp.flags + "g";
const re = new RegExp(regexp, flags);
let match;
while (match = re.exec(str)) {
yield match;
}
}
A copy of the original regexp is created; this is to avoid side-effects due to the mutation of the lastIndex
property when going through the multple matches.
Also, we need to ensure the regexp has the global flag to avoid an infinite loop.
I'm also happy to see that even this StackOverflow question was referenced in the discussions of the proposal.
2017 — 2021 update
Since 2009 when this question was asked, JavaScript has evolved significantly. All other answers are now obsolete or overly complicated. Here is the current best practice:
function sleep(ms) {
return new Promise(resolve => setTimeout(resolve, ms));
}
async function demo() {
console.log('Taking a break...');
await sleep(2000);
console.log('Two seconds later, showing sleep in a loop...');
// Sleep in loop
for (let i = 0; i < 5; i++) {
if (i === 3)
await sleep(2000);
console.log(i);
}
}
demo();
This is it. await sleep(<duration>)
.
Or as a one-liner:
await new Promise(r => setTimeout(r, 2000));
Note that,
await
can only be executed in functions prefixed with the async
keyword, or at the top level of your script in an increasing number of environments.
await
only pauses the current async
function. This means it's not blocking the execution of the rest of the script, which is what you want in the vast majority of the cases. If you do want a blocking construct, see this answer using Atomics
.wait
, but note that most browsers will not allow it on the browser's main thread.
Two new JavaScript features (as of 2017) helped write this "sleep" function:
Compatibility
If for some weird reason you're using Node older than 7 (which has reached end of life), or are targeting old browsers, async
/await
can still be used via Babel (a tool that will transpile JavaScript + new features into plain old JavaScript), with the transform-async-to-generator
plugin.
Best Answer
It always a good practice to pass radix with parseInt -
For decimal -
If the radix parameter is omitted, JavaScript assumes the following:
(Reference)