cover

Understand what Promise objects are

In the project, there will be various asynchronous operations. If there are asynchronous operations in the callback of an asynchronous operation, there will be a callback pyramid.

Like the following

// Simulate to get the code, then pass the code to the background, get userinfo after success, and then pass userinfo to the background
// Sign in
wx.login({
    success: res => {
        let code = res.code
        // request
        imitationPost({
            url: '/test/loginWithCode',
            data: {
                code
            },
            success: data => {
                // Get userInfo
                wx.getUserInfo({
                    success: res => {
                        let userInfo = res.userInfo
                        // request
                        imitationPost({
                            url: '/test/saveUserInfo',
                            data: {
                                userInfo
                            },
                            success: data => {
                                console.log(data)
                            },
                            fail: res => {
                                console.log(res)
                            }
                        })
                    },
                    fail: res => {
                        console.log(res)
                    }
                })
            },
            fail: res => {
                console.log(res)
            }
        })
    },
    fail: res => {
        console.log(res)
    }
})

Here's how to simplify the code with Promise

Because the asynchronous api of wechat applets is in the form of success and fail, everyone encapsulates such a method:

promisify.js

module.exports = (api) => {
    return (options, ...params) => {
        return new Promise((resolve, reject) => {
            api(Object.assign({}, options, { success: resolve, fail: reject }), ...params);
        });
    }
}

First look at the simplest:

// Get system information
wx.getSystemInfo({
    success: res => {
        // success
        console.log(res)
    },
    fail: res => {

    }
})

After simplification with promise.js above:

const promisify = require('./promisify')
const getSystemInfo = promisify(wx.getSystemInfo)

getSystemInfo().then(res=>{
    // success
    console.log(res)
}).catch(res=>{

})

getSystemInfo

You can see that there is less indentation in the simplified callback, and the callback function is reduced from 9 lines to 6 lines.

Simplification effect of callback pyramid

So let's take a look at the first callback pyramid

const promisify = require('./promisify')
const login = promisify(wx.login)
const getSystemInfo = promisify(wx.getSystemInfo)

// Sign in
login().then(res => {
    let code = res.code
    // request
    pImitationPost({
        url: '/test/loginWithCode',
        data: {
            code
        },
    }).then(data => {
        // Get userInfo
        getUserInfo().then(res => {
            let userInfo = res.userInfo
            // request
            pImitationPost({
                url: '/test/saveUserInfo',
                data: {
                    userInfo
                },
            }).then(data => {
                console.log(data)
            }).catch(res => {
                console.log(res)
            })
        }).catch(res => {
            console.log(res)
        })
    }).catch(res => {
        console.log(res)
    })
}).catch(res => {
    console.log(res)
})

Simplified callback

You can see that the simplification effect is very obvious.

It is also applicable to web pages or nodejs.

Reference resources

• Promise object

source code

• tomfriwel/MyWechatAppDemo The promise page of