优秀装饰器源码学习（三）

import { mixin } from '../index'
const obj1 = {
    logA() {
        console.log(this.a);
    }
}
const obj2 = {
    printKeys() {
        console.log(Object.keys(this));
    }
}

@mixin(obj1, obj2)
class Test {
    public a = 1
}

const t: any = new Test()

t.logA() // 1
t.printKeys() // ['a']

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function handleClass(target, mixins) {
    if (!mixins.length) {
        throw new SyntaxError(`@mixin() class ${target.name} requires at least one mixin as an argument`);
    }
}
export default function mixin(...objs) {
    return function (target) {
        return handleClass(target, objs)
    }
}

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/**
 * 获取对象上的每个属性的描述符
 */
function getOwnPropertyDescriptors(obj) {
    const descs = {};
    Object.getOwnPropertyNames(obj).forEach(key => {
        descs[key] = Object.getOwnPropertyDescriptor(obj, key)
    })
    return descs;
}

function handleClass(target, mixins) {
    if (!mixins.length) {
        throw new SyntaxError(`@mixin() class ${target.name} requires at least one mixin as an argument`);
    }
    for (let i = 0; i < mixins.length; i++) {
        const descs = getOwnPropertyDescriptors(mixins[i])
        const keys = Object.getOwnPropertyNames(mixins[i])

        for (let j = 0; j < keys.length; j++) {
            const key = keys[j];
            if (!target.prototype.hasOwnProperty(key)) {
                Object.defineProperty(target.prototype, key, descs[key])
            }
        }
    }
}

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import { lazyInitialize } from "..";

function getMaxArray(str=''){
    console.log(str,'init huge array');
    return new Array(100)
}

class Test{
    @lazyInitialize(()=>getMaxArray('a'))
    public a
    public b = getMaxArray('b')
}

const t = new Test()
const k = new Test()
k.a

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function createDefaultSetter(key) {
    return function set(newValue) {
        Object.defineProperty(this, key, {
            configurable: true,
            writable: true,
            enumerable: true,
            value: newValue
        });
        return newValue;
    };
}

export default function lazyInitialize(initializer): any {
    let t
    return function (target, key) {
        return {
            get() {
                t = t === undefined? initializer.call(this) : t
                return t;
            },
            set: createDefaultSetter(key)
        }
    }
}

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优秀装饰器源码学习（三）

优秀装饰器源码学习（三）

# 优秀装饰器源码学习（三）

# 前言

# @mixin

# 使用示例

# 函数结构

# 实现原理

# handleClass的完整实现

# lazyInitialize

# 使用示例

# 实现原理

# 函数实现

# 未完待续