feat: 最简单的promise异步调用链

Author: sl1673495

promise-easy.js

@@ -0,0 +1,60 @@
+/**
+ * 仅实现异步链式调用的简化版
+ */
+
+function Promise(excutor) {
+  var self = this
+  self.status = "pending" // Promise当前的状态
+  self.data = undefined // Promise的值
+  self.onResolvedCallback = [] // Promise resolve时的回调函数集，因为在Promise结束之前有可能有多个回调添加到它上面
+
+  function resolve(value) {
+    setTimeout(() => {
+      if (self.status === "pending") {
+        self.status = "resolved"
+        self.data = value
+        self.onResolvedCallback.forEach(callback => callback(value))
+      }
+    })
+  }
+
+  excutor(resolve.bind(self))
+}
+
+Promise.prototype.then = function(onResolved) {
+  var self = this
+
+  return new Promise(resolve => {
+    self.onResolvedCallback.push(function() {
+      var result = onResolved(self.data)
+      if (result instanceof Promise) {
+        result.then(resolve)
+      } else {
+        resolve(result)
+      }
+    })
+  })
+}
+
+new Promise(resolve => {
+  setTimeout(() => {
+    resolve(1)
+  }, 500)
+})
+  .then(res => {
+    console.log(res)
+    return new Promise(resolve => {
+      setTimeout(() => {
+        resolve(2)
+      }, 500)
+    })
+  })
+  .then(res => {
+    console.log(res)
+    return new Promise(resolve => {
+      setTimeout(() => {
+        resolve(3)
+      }, 500)
+    })
+  })
+  .then(console.log)