遍历数组并使用JS汇总所有值

Question

as the title says i'm trying to sum up using a for loop to iterate over an array. can you give me some pointers as to where i'm going wrong here. i am returning the value NaN.

var total = 0;

function sum(input) {
    for (idx=0; idx<=input; idx++) {
        total += input[idx];
    }
    return total;
}

Answer 1

You actually don't need a loop to do this in modern browsers, you can use the Array.reduce function:

var sum = input.reduce(function(a,b){
    return a+b;
}, 0);

Answer 2

You need ot declare total into function and also you need to declare idx. Another thing that instead of writing idx <= input.length you have to write idx <= input.length - 1 . Since last index will be undefined.

Try

function sum(input) {
    total = 0;
    for (var idx = 0; idx <= input.length - 1; idx++) {
        total += input[idx];
    }
    return total;
}

Answer 3

variable total is not declared!

function sum(input) {
    var total = 0;
    for (idx=0; idx <= input.length; idx++) {
        total += input[idx];
    }
    return total;
}

Answer 4

Problem which result in NaN is because of your array traversing array till end, rather than from indices 0 to input.length-1 Try this: http://jsfiddle.net/t9tfofxv/

var total = 0;
function sum(input) {
for (var idx=0; idx< input.length; idx++) {
    total += input[idx];
}
return total;
}
var s=sum([1,2,3,4]);
alert(s);

Answer 5

Declare the variable total inside the function, and also use input.length-1 to define the loop's range:

function sum(input) {
    var total = 0;
    for (idx=0; idx <= input.length-1; idx++) {
        total += input[idx];
    }
    return total;
}

Answer 6

You are using input both as an integer, and as an array of values. Probably you mean for( var idx = 0; idx < input.length; ++idx )... .