我有一个深对象:
{
"something": "Homepage",
"else": [
"[replaceme]",
"[replaceme]"
],
"aside": "[replaceme]",
"test": {
"test": {
"testing": [
"[replaceme]",
"[replaceme]",
"variable",
{
"testing": {
"testing": {
"something": "[replaceme]",
"testing": {
"testing": [
"[replaceme]",
"[replaceme]"
]
}
}
}
}
]
}
}
}
现在我需要将每次出现的 [replaceme]
替换为来自异步函数的内容。每次都不一样。
我以为我减少了对象的每个级别并返回了一个 promise 链。
这是我到目前为止得到的:
const IterateObject = ( object ) => {
return new Promise( ( resolve, reject ) => {
Object.keys( object ).reduce( ( sequence, current ) => {
const key = current;
return sequence.then( () => {
return new Promise( ( resolve, reject ) => {
if( typeof object[ key ] === 'object' ) {
IterateObject( object[ key ] )
.then( result => {
newObject[ key ] = result;
});
// ^----- How do I add the next level when it returns a promise?
}
else {
resolve( newObject[ key ] )
}
});
});
}, Promise.resolve())
.catch( error => reject( error ) )
.then( () => {
console.log('done');
resolve();
});
});
}
问题
解决这个问题的最佳方法是什么?也许 promise 链不是正确的工具?
最佳答案
不要尝试在单个函数中执行此操作。这可能会导致称为 The Collection Kerfuffle 的常见反模式。将此作业拆分为独立的 block :深度遍历对象、异步 setter 等。通过遍历对象收集所有待处理的 promise ,并使用 Promise.all
// traverse object obj deep using fn iterator
const traverse = (obj, fn) => {
const process = (acc, value, key, object) => {
const result =
Array.isArray(value)
? value.map((item, index) => process(acc, item, index, value))
: (
typeof value === 'object'
? Object.keys(value).map(key => process(acc, value[key], key, value))
: [fn(value, key, object)]
)
return acc.concat(...result)
}
return process([], obj)
}
// fake async op
const getAsync = value => new Promise(resolve => setTimeout(resolve, Math.random()*1000, value))
// useful async setter
const setAsync = (target, prop, pendingValue) => pendingValue.then(val => target[prop] = val)
// traverse object obj deep using fn iterator
const traverse = (obj, fn) => {
const process = (acc, value, key, object) => {
const result =
Array.isArray(value)
? value.map((item, index) => process(acc, item, index, value))
: (
typeof value === 'object'
? Object.keys(value).map(key => process(acc, value[key], key, value))
: [fn(value, key, object)]
)
return acc.concat(...result)
}
return process([], obj)
}
// set async value
const replace = (value, prop, target) => {
if( value === '[replaceme]') {
return setAsync(target, prop, getAsync(`${prop} - ${Date.now()}`))
}
return value
}
const tmpl = {
"something": "Homepage",
"else": [
"[replaceme]",
"[replaceme]"
],
"aside": "[replaceme]",
"test": {
"test": {
"testing": [
"[replaceme]",
"[replaceme]",
"variable",
{
"testing": {
"testing": {
"something": "[replaceme]",
"testing": {
"testing": [
"[replaceme]",
"[replaceme]"
]
}
}
}
}
]
}
}
}
Promise.all(
traverse(tmpl, replace)
)
.then(() => console.log(tmpl))
.catch(e => console.error(e))
或者您可能想看一下 async/await
,它允许您编写更多“类似同步”的代码。但是这种实现会导致顺序执行。
// using async/await
const fillTemplate = async (tmpl, prop, object) => {
if(Array.isArray(tmpl)) {
await Promise.all(tmpl.map((item, index) => fillTemplate(item, index, tmpl)))
}
else if(typeof tmpl === 'object') {
await Promise.all(Object.keys(tmpl).map(key => fillTemplate(tmpl[key], key, tmpl)))
}
else {
await replace(tmpl, prop, object)
}
}
const tmpl = {
"something": "Homepage",
"else": [
"[replaceme]",
"[replaceme]"
],
"aside": "[replaceme]",
"test": {
"test": {
"testing": [
"[replaceme]",
"[replaceme]",
"variable",
{
"testing": {
"testing": {
"something": "[replaceme]",
"testing": {
"testing": [
"[replaceme]",
"[replaceme]"
]
}
}
}
}
]
}
}
}
// fake async op
const getAsync = value => new Promise(resolve => setTimeout(resolve, Math.random()*1000, value))
// useful async setter
const setAsync = (target, prop, pendingValue) => pendingValue.then(val => target[prop] = val)
// set async value
const replace = (value, prop, target) => {
if( value === '[replaceme]') {
return setAsync(target, prop, getAsync(`${prop} - ${Date.now()}`))
}
return value
}
// using async/await
const fillTemplate = async (tmpl, prop, object) => {
if(Array.isArray(tmpl)) {
await Promise.all(tmpl.map((item, index) => fillTemplate(item, index, tmpl)))
}
else if(typeof tmpl === 'object') {
await Promise.all(Object.keys(tmpl).map(key => fillTemplate(tmpl[key], key, tmpl)))
}
else {
await replace(tmpl, prop, object)
}
}
Promise
.resolve(fillTemplate(tmpl))
.then(() => console.log(tmpl))
.catch(e => console.error(e))
关于javascript - 为深层嵌套对象构建 promise 链,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/44667629/