https://www.cnblogs.com/zhuzhenwei918/p/6915451.html vue中promise的使用
https://segmentfault.com/a/1190000016680014 vue+axios+promise实际开发用法
https://www.youtube.com/watch?v=s6SH72uAn3Q
前因(問題)
Vue访问本地json时会出现TypeError: Cannot read property '0' of undefined
正解
在JSON请求回来的时候已经渲染页面了，此时你给的page3的默认值是[]，所以page3.page3_a是undefined，你再使用[0]当然就会报错了，你需要在初始化data的时候，把需要的结构都初始化，代码如下：
data: function() {
return {
page3: {
page3_a: [{
title: []
}]
}
}
}
这样在数据没有回来的时候访问page3.page3_a[0].title才不会报错。
或是
index_content:{
announce:[{
info:''
}],
footer_image:[{
info:''
}],
footer_text:[{
info:''
}],
ftd_text:[{
info:''
}],
image:[{
info:''
},{
info:''
},{
info:'' //就是這個啦！
}],
}
這樣index_content.image[2].info就不會出錯誤訊息！
※結果搜出promise順便了解下
可以快速理解的例子
const promise = new Promise((resolve, reject) => {
setTimeout(() =>{
const r =Math.random();
if(r >0.5){
resolve(r)
}else{
reject(r)
}
},1000)
})
promise.then((value) => {
console.log('成功',value)
}).catch((error) => {
console.log('失敗', error)
})
基础篇
let promiseToCleanTheRoom = new Promise(function(resolve, reject) {
//cleaning the room
let isClean = false;
if (isClean) {
resolve('Clean');
} else {
reject('not Clean');
}
});
promiseToCleanTheRoom.then(function(fromResolve) {
console.log('the room is' + fromResolve);
}).catch(function(fromReject){
console.log('the room is' + fromReject);
})
//结果：the room is not Clean
复杂篇
let cleanRoom = function() {
return new Promise(function(resolve, reject) {
resolve('Cleaned The Room');
});
};
let removeGarbage = function(message) {
return new Promise(function(resolve, reject) {
resolve(message + ' remove Garbage');
});
};
let winIcecream = function(message) {
return new Promise(function(resolve, reject) {
resolve( message + ' won Icecream');
});
};
cleanRoom().then(function(result){
return removeGarbage(result);
}).then(function(result){
return winIcecream(result);
}).then(function(result){
console.log('finished ' + result);
})
//结果：finished Cleaned The Room remove Garbage won Icecream
进阶篇
阵列里全部执行完才触发
Promise.all ( [ cleanRoom(), removeGarbage(), winIcecream() ] ).then(funtion(){
console.log('all finished!')
})
阵列里只要有一个执行完就触发(例如接收同样的data，只要拿到一个就可以往后执行)
Promise.race ( [ cleanRoom(), removeGarbage(), winIcecream() ] ).then(funtion(){
console.log('one of them is finished')
})
