javascript:Async/await in.replace
我使用async/await函数的方式如下javascript:Async/await in.replace,javascript,async-await,es6-promise,ecmascript-2016,Javascript,Async Await,Es6 Promise,Ecmascript 2016,我使用async/await函数的方式如下 async function(){ let output = await string.replace(regex, async (match)=>{ let data = await someFunction(match) console.log(data); //gives correct data return data }) return output; } 但返回的数据是promise对象。只是对它
async function(){
let output = await string.replace(regex, async (match)=>{
let data = await someFunction(match)
console.log(data); //gives correct data
return data
})
return output;
}
但返回的数据是promise对象。只是对它在回调函数中的实现方式感到困惑。因此,没有需要承诺的替换重载。因此,只需重申您的代码:
async function(){
let data = await someFunction();
let output = string.replace(regex, data)
return output;
}
当然,如果需要使用匹配值传递给异步函数,事情会变得有点复杂:
var sourceString = "sheepfoohelloworldgoocat";
var rx = /.o+/g;
var matches = [];
var mtch;
rx.lastIndex = 0; //play it safe... this regex might have state if it's reused
while((mtch = rx.exec(sourceString)) != null)
{
//gather all of the matches up-front
matches.push(mtch);
}
//now apply async function someFunction to each match
var promises = matches.map(m => someFunction(m));
//so we have an array of promises to wait for...
//you might prefer a loop with await in it so that
//you don't hit up your async resource with all
//these values in one big thrash...
var values = await Promise.all(promises);
//split the source string by the regex,
//so we have an array of the parts that weren't matched
var parts = sourceString.split(rx);
//now let's weave all the parts back together...
var outputArray = [];
outputArray.push(parts[0]);
values.forEach((v, i) => {
outputArray.push(v);
outputArray.push(parts[i + 1]);
});
//then join them back to a string... voila!
var result = outputArray.join("");
不处理异步回调,您不能将其与返回承诺的替换程序一起使用
但是,我们可以编写自己的replace
函数来处理承诺:
async function(){
return string.replace(regex, async (match)=>{
let data = await someFunction(match)
console.log(data); //gives correct data
return data;
})
}
function replaceAsync(str, re, callback) {
// http://es5.github.io/#x15.5.4.11
str = String(str);
var parts = [],
i = 0;
if (Object.prototype.toString.call(re) == "[object RegExp]") {
if (re.global)
re.lastIndex = i;
var m;
while (m = re.exec(str)) {
var args = m.concat([m.index, m.input]);
parts.push(str.slice(i, m.index), callback.apply(null, args));
i = re.lastIndex;
if (!re.global)
break; // for non-global regexes only take the first match
if (m[0].length == 0)
re.lastIndex++;
}
} else {
re = String(re);
i = str.indexOf(re);
parts.push(str.slice(0, i), callback.apply(null, [re, i, str]));
i += re.length;
}
parts.push(str.slice(i));
return Promise.all(parts).then(function(strings) {
return strings.join("");
});
}
对于某些异步替换,这是一个易于使用和理解的函数:
async function replaceAsync(str, regex, asyncFn) {
const promises = [];
str.replace(regex, (match, ...args) => {
const promise = asyncFn(match, ...args);
promises.push(promise);
});
const data = await Promise.all(promises);
return str.replace(regex, () => data.shift());
}
它会执行两次替换功能,因此如果您要处理一些繁重的操作,请小心。不过,对于大多数用法来说,它非常方便
像这样使用它:
replaceAsync(myString, /someregex/g, myAsyncFn)
.then(replacedString => console.log(replacedString))
或者这个:
const replacedString = await replaceAsync(myString, /someregex/g, myAsyncFn);
不要忘记您的myAsyncFn
必须返回一个承诺
异步函数的一个示例:
async function myAsyncFn(match) {
// match is an url for example.
const fetchedJson = await fetch(match).then(r => r.json());
return fetchedJson['date'];
}
function myAsyncFn(match) {
// match is a file
return new Promise((resolve, reject) => {
fs.readFile(match, (err, data) => {
if (err) return reject(err);
resolve(data.toString())
});
});
}
async
函数的返回值始终是一个Promise对象,该对象使用返回的输出进行解析(或使用抛出的错误进行拒绝)。您是否想知道为什么output
是一个Promise?我不清楚你的问题是什么。请注意,如果string.replace
是字面上的string.prototype.replace
,那么这将不起作用.replace
希望回调函数是正常函数,而不是异步函数。我已更新了问题。我需要将匹配的元素传递给函数,这样做是不可能的。@ritz078我想你可能错过了这个。也许我的编辑更有用?这只在使用replace迭代匹配时有效。这对替换不起作用,但它确实起作用。它迭代,替换。我真的很喜欢这个解决方案,很好很简单!