feat: Promise实现

Author: Z1hgq

js/_Promise.js

@@ -0,0 +1,126 @@
+function _Promise(fn) {
+    const self = this;
+    self.status = 'pending'; // 状态
+    self.data = undefined; // 结果
+    self.onFulfilledCallback = [];
+    self.onRejectedCallback = [];
+
+    function resolve(value) {
+        self.status = 'fulfilled';
+        self.data = value;
+        setTimeout(() => {
+            for (const callback of self.onFulfilledCallback) {
+                callback(value)
+            }
+        })
+    }
+
+    function reject(reason) {
+        self.status = 'rejected';
+        self.data = reason;
+        setTimeout(() => {
+            for (const callback of self.onRejectedCallback) {
+                callback(reason)
+            }
+        })
+    }
+
+    try {
+        fn(resolve, reject);
+    } catch (error) {
+        reject(error);
+    }
+
+}
+
+_Promise.prototype.then = function (onFulfilled, onRejected) {
+    const self = this;
+
+    onFulfilled = typeof onFulfilled === 'function' ? onFulfilled : () => { };
+    onRejected = typeof onRejected === 'function' ? onRejected : () => { };
+
+    if (self.status === 'fulfilled') {
+        return new _Promise((resolve, reject) => {
+            try {
+                const res = onFulfilled(self.data);
+                if (res instanceof _Promise) {
+                    res.then(resolve, reject);
+                } else {
+                    resolve(res);
+                }
+            } catch (error) {
+                reject(error)
+            }
+        });
+    } else if (self.status === 'rejected') {
+        return new _Promise((resolve, reject) => {
+            try {
+                const res = onRejected(self.data);
+                if (res instanceof _Promise) {
+                    res.then(resolve, reject);
+                } else {
+                    reject(res);
+                }
+            } catch (error) {
+                reject(error)
+            }
+        });
+    } else if (self.status === 'pending') {
+        return new _Promise((resolve, reject) => {
+            self.onFulfilledCallback.push(
+                function () {
+                    try {
+                        const res = onFulfilled(self.data);
+                        if (res instanceof _Promise) {
+                            res.then(resolve, reject);
+                        } else {
+                            resolve(res);
+                        }
+                    } catch (error) {
+                        reject(error)
+                    }
+                }
+            )
+            self.onRejectedCallback.push(
+                function () {
+                    try {
+                        const res = onRejected(self.data);
+                        if (res instanceof _Promise) {
+                            res.then(resolve, reject);
+                        } else {
+                            reject(res);
+                        }
+                    } catch (error) {
+                        reject(error)
+                    }
+                }
+            )
+        });
+    }
+}
+
+// 顺便实现一下catch方法
+_Promise.prototype.catch = function (onRejected) {
+    return this.then(null, onRejected);
+}
+
+
+const p = new _Promise(function (resolve, reject) {
+    setTimeout(function () {
+        resolve(1);
+    }, 2000);
+});
+
+p.then(function (v) {
+    console.log(v);
+    return 2;
+}).then(function (v) {
+    console.log(v);
+    return new _Promise(function (resolve, reject) {
+        setTimeout(function () {
+            resolve(3);
+        }, 3000);
+    });
+}).then(function (v) {
+    console.log(v);
+});