JavaScript大位数相加减

    function arrayAdd(number, addNumber) {
        var numberArr = number.toString().split('');
        var addNumberArr = addNumber.toString().split('');
        var temporary = []; //临时值
        //比较大小长度，numberArr的值要比addNumberArr的值要大
        if (addNumberArr.length > numberArr.length) {
            //实现两值的调换
            temporary = numberArr;
            numberArr = addNumberArr;
            addNumberArr = temporary;
        } else if (addNumberArr.length === numberArr.length) {
            //比较数组里面的值
            var flag = true; //默认numberArr比addNumberArr的值大
            var length = addNumberArr.length;
            for (var i = 0; i < length; i++) {
                var numObj = parseInt(numberArr[i]);
                var addObj = parseInt(addNumberArr[i]);
                if (numObj > addObj) {
                    break;
                } else if (numObj < addObj) {
                    flag = false;
                    break;
                }
            }
            if (!flag) {
                //实现两值的调换
                temporary = numberArr;
                numberArr = addNumberArr;
                addNumberArr = temporary;
            }
        }

        for (var i = numberArr.length - 1; i >= 0; i--) { //从后面算起
            var numObj = parseInt(numberArr[i]);
            var addObj = parseInt(addNumberArr[i - (numberArr.length - addNumberArr.length)]);

            if (!isNaN(addObj)) {
                if (numObj + addObj >= 10) {
                    numberArr[i] = numObj + addObj - 10;

                    if (i - 1 < 0) {
                        //如果是90+10的话,超出了数组的范围
                        numberArr.splice(0, 0, 1);
                    } else {
                        for (var j = i - 1; j >= 0; j--) { //从后面算起
                            var obj = parseInt(numberArr[j]);
                            if (obj + 1 === 10) {
                                numberArr[j] = 0;
                                if (j === 0) {
                                    //循环到最后一个，将numberArr数组加上最前面1
                                    // splice(position, numberOfItemsToRemove, item)
                                    // 拼接函数(索引位置, 要删除元素的数量, 元素)
                                    numberArr.splice(0, 0, 1);
                                    i++; //数组的长度已经改变,将循环再次加多一次
                                    break;
                                }
                            } else {
                                numberArr[j] = obj + 1;
                                break;
                            }
                        }
                    }
                } else {
                    numberArr[i] = numObj + addObj;
                }
            }
        }
        return numberArr.join("");
    }

    //判断大小,返回true或者false
    function arrayCompare(firstNumber, sendNumber) {
        var firstNumberArr = firstNumber.toString().split('');
        var sendNumberArr = sendNumber.toString().split('');
        //比较大小长度，firstNumberArr的值要比sendNumberArr的值要大
        if (firstNumberArr.length > sendNumber.length) {
            return true;
        } else if (sendNumberArr.length > firstNumberArr.length) {
            //实现两值的调换
            return false;
        } else if (sendNumberArr.length === firstNumberArr.length) {
            //比较数组里面的值
            var flag = true; //默认firstNumberArr比sendNumberArr的值大
            var length = sendNumberArr.length;
            for (var i = 0; i < length; i++) {
                var numObj = parseInt(firstNumberArr[i]);
                var addObj = parseInt(sendNumberArr[i]);
                if (numObj > addObj) {
                    break;
                } else if (numObj < addObj) {
                    flag = false;
                    break;
                }
            }
            if (!flag) {
                //实现两值的调换
                return false;
            } else {
                return true;
            }
        }
    }

    //startNumber是减数,endNumber是正减除数
    function arrayDiff(startNumber, endNumber) {
        var startNumberArr = startNumber.toString().split('');
        var endNumberArr = endNumber.toString().split('');
        var temporary = []; //临时值
        var positiveNumber = true;//如果startNumber大于endNumber的话,就返回负值
        //比较大小长度，endNumberArr 的值要比startNumberArr 的值要大
        if (startNumberArr.length > endNumberArr.length) {
            //实现两值的调换
            temporary = endNumberArr;
            endNumberArr = startNumberArr;
            startNumberArr = temporary;
            positiveNumber = false;
        } else if (endNumberArr.length === startNumberArr.length) {
            //比较数组里面的值
            var flag = true; //默认endNumberArr比startNumberArr的值大
            var length = startNumberArr.length;
            for (var i = 0; i < length; i++) {
                var endObj = parseInt(endNumberArr[i]);
                var startObj = parseInt(startNumberArr[i]);
                if (endObj > startObj) {
                    break;
                } else if (endObj < startObj) {
                    flag = false;
                    break;
                }
            }
            if (flag === false) {
                //实现两值的调换
                temporary = endNumberArr;
                endNumberArr = startNumberArr;
                startNumberArr = temporary;
                positiveNumber = false;
            }
        }

        for (var i = endNumberArr.length - 1; i >= 0; i--) { //从后面算起
            var endObj = parseInt(endNumberArr[i]);
            var startObj = parseInt(startNumberArr[i - (endNumberArr.length - startNumberArr.length)]);
            if (!isNaN(startObj)) {
                if (endObj - startObj < 0) {
                    endNumberArr[i] = endObj + 10 - startObj;
                    for (var j = i - 1; j >= 0; j--) { //从后面算起
                        var obj = parseInt(endNumberArr[j]);
                        if (obj === 0) {
                            endNumberArr[j] = 9;
                        }
                        else {
                            endNumberArr[j] = obj - 1;
                            break;
                        }
                    }
                }
                else {
                    endNumberArr[i] = endObj - startObj;
                }
            }
        }

        //判断前面是否为0,例如012,从前面算起
        for (var i = 0; i < endNumberArr.length; i++) {
            var obj = endNumberArr[i];
            if (obj !== null) {
                if (obj === 0) {
                    endNumberArr.splice(i, 1);
                    i--;
                }
                else {
                    break;
                }
            }
        }

        var result = endNumberArr.join("");
        if (!positiveNumber) {
            result = "-" + result;
        }
        return result;
    }

    //传进去的时候必须是字符串,不然会被计算机默认为number类型,从而数字发生变化
    var b = arrayDiff("21111111111111118", "21111111111111119");
    //alert(b);