手写apply

    Function.prototype.myApply = function (thisArg, argArray) {
        const fn = Symbol('fn')
        thisArg[fn] = this
        const res = thisArg[fn](...argArray)
        delete thisArg[fn]
        return res
    }


    const person = {
        name: 'mandy',
        age: 21
    }

    function fun(numA, numB) {
        console.log(this);
        console.log(numA, numB);
        return numA + numB;
    }

    const result = fun.myApply(person, [1, 2]);
    console.log('myApply - result:' + result);

    const result2 = fun.apply(person, [3, 4]);
    console.log('apply - result:' + result2);

</script>

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