function _Promise(fn) {
var that = this;
this.status = 'pending';
this.value = '';
this.error = '';
this.onSuccess = [];
this.onReject = [];
function resolve(value) {
if (that.status == 'pending') {
that.value = value;
that.status = 'success';
that.onSuccess.forEach(fu => fu(value))
}
}
function reject(value) {
if (that.status == 'pending') {
that.error = value;
that.status = 'reject';
that.onReject.forEach(fu => fu(value))
}
}
try {
fn(resolve, reject)
} catch (e) {
resolve(e)
}
}
_Promise.prototype.then = function(onResolve, onReject) {
if (this.status === 'success') {
typeof onResolve === 'function' ? onResolve(this.value) : ''
} else if (this.status === 'reject') {
typeof onReject === 'function' ? onReject(this.error) : ''
} else if (this.status === 'pending') {
typeof onResolve === 'function' ? this.onSuccess.push(onResolve) : ''
typeof onReject === 'function' ? this.onReject.push(onReject) : ''
}
}调用测试
new _Promise((resolve, reject) => {
setTimeout(()=>{
resolve('success')
},500)
}).then(res => {
console.log(res)
}, err => {
console.log(err)
})结果：
