JavaScript Symbol.iterator

粗略的实现Array的功能

interface MyArray<T> {
    [key: number]: T
}
class MyArray<T> {
    constructor() {
        // Object.defineProperties(this, {
        //     length: {
        //         enumerable: false
        //     }
        // });
        // @ts-ignore
        Object.defineProperties(this.__proto__, {
            push: {
                enumerable: false
            },
            from: {
                enumerable: false
            }
        });
    }
    [Symbol.iterator](){　
        let i = 0;
        let len = this.length;
        return {
            next: () => {
                return { value: this[i], done: i++ >= len };
            }
        }
    }
    /**
     * push
     */
    public push(val: T) {
        this[this.length] = val;
    }
    /**
     * from
     */
    public from(val: T[]) {
        for(let i = 0; i < this.length; i++) {
            delete this[i];
        }
        for(let i =0;i< val.length; i++) {
            this[i] = val[i];
        }
    }
    get length() {
        console.log('----')
        let i = 0;
        for(let key in this) {
            i++;
        }
        return i;
    }
    set length(_: any) {

    }
}
let arr = new MyArray();
arr[0] = '123';
arr[1] = '456';
arr.push('678');
console.log(arr);
console.log(arr.length);
for(let item of arr) {
    console.log('-----1')
    console.log(item)
}
for(let item of arr) {
    console.log('-----1')
    console.log(item)
}
for(let key in arr) {
    console.log('key:',key);
}
arr.from(['a', 'b','c'])