js实现reduce, forEach, map, filter

[h476564406]

<script>
    // myReduce
    function myReduce(array, callback, initValue = 0) {
        let accumulator = initValue;

        for (let index = 0; index < array.length; index++) {
            const element = array[index];

            accumulator = callback.apply(null, [accumulator].concat(array[index]))
        }

        return accumulator;
    }

    const array2 = [1, 2, 3, 4];
    const reducer = (accumulator, currentValue) => accumulator + currentValue;

    // 1 + 2 + 3 + 4
    console.log('myReduce1', myReduce(array2, reducer));
    // expected output: 10

    // 5 + 1 + 2 + 3 + 4
    console.log('myReduce2', myReduce(array2, reducer, 5));
    // expected output: 15

    // myForeach
    function myForeach(array, callback) {
        for (let index = 0; index < array.length; index++) {
            const element = array[index];
            callback(element, index);
        }
    }

    var array1 = ['a', 'b', 'c'];

    myForeach(array1, function (element) {
        console.log('myForeach', element);
    });

    // myMap
    function myMap(array, callback) {
        const res = [];

        for (let index = 0; index < array.length; index++) {
            const element = array[index];
            res.push(callback(element, index));
        }

        return res;
    }

    var array1 = [1, 4, 9, 16];

    const map1 = myMap(array1, x => x * 2);

    console.log('myMap', map1);

    // myFilter
    function myFilter(array, callback) {
        const res = [];

        for (let index = 0; index < array.length; index++) {
            const element = array[index];
            if (!!callback(element, index)) {
                res.push(element);
            }
        }

        return res;
    }

    var words = ['spray', 'limit', 'elite', 'exuberant', 'destruction', 'present'];

    const filter1 = myFilter(words, word => word.length > 6);

    console.log('myFilter', filter1);
</script>