Javascript: Loop, iterate, and add new values

Question

Goal: Gather all the results from a loop (that loops through JSON object array) and add those values together to produce the overall number of credits for a user. Every time they take a course, they receive credit, but right now, I need to figure out how to add them together. I am new to Javascript and am trying to figure out how to create a function that continually updates (via a for loop), so that I can produce it via HTML in the web page.

I was looking at this stack example that loops together values (for a game) and tried to mimic it. I was also looking at the for loop example via this JS tutorial.

var sum = 0; for (var i = 1; i <= 50; i++) {    sum = sum + i; }
alert("Sum = " + sum);    // => Sum = 1275

It consists of three parts, separated by semicolons. The first is the initializer (var i = 1) which initializes the loop and is executed only once at the start. The second is a test condition (i <= 50). When a conditional expression evaluates to true, the body of the loop is executed. When false, the loop terminates. The third part is an updater (i++) which is invoked after each iteration. The updater typically increments or decrements the loop counter.

My Code:

    //Function that returns HTML for successfully retrieved results
    function resultsHTML(JSONResponseObjectArray) {
        var ddObjectArray = JSONResponseObjectArray;
        var resultString = '';
        //Loop through JSON Object Array
        for(eeIndex in ddObjectArray) {
            var creditHours = ddObjectArray[eeIndex].creditHours;

        resultString += ceHTML(creditHours);
        console.log("credit hours: " + creditHours);

}

}

    function addCredits(){
      var result = 0;
        for (var i = 0; i <= 0; i++){
        result = creditHours + i;
        }
        return result;
          console.log('new results ' + result);
      }

Output of Array (via console):

credit hours: null
list.js:114 credit hours: 4
list.js:114 credit hours: 6
list.js:114 credit hours: null
list.js:114 credit hours: 4
list.js:114 credit hours: null

Couple small issues. First off, your addCredits function is inside of your other function. Second, resultsHTML isn't closed. Third, your console.log won't happen because it's after a return which ends the function. — Kelderic
– Kelderic, Commented Mar 7, 2017 at 17:33

thesayhey · Accepted Answer · 2017-03-07 18:21:46Z

2

You'd usually use reduce to sum the values in an array of objects (what your data will be - assumption as you don't show data). Just call the following addCredits() function with your array, replace b.credit with the property that holds the number to sum:

var creditHours = [{
  creditHours: 1
}, {
  creditHours: 2
}];

function addCredits(data) {
  return data.reduce(function(a, b) {
    a += b.creditHours;
    return a;
  }, 0)
}
console.log(addCredits(creditHours));

edited Mar 7, 2017 at 18:21

thesayhey

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answered Mar 7, 2017 at 17:34

baao

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16 Comments

thesayhey Over a year ago

I notice that the ` console.log("credit hours: " + creditHours);` from the first function is not working for the new function to add together.

baao Over a year ago

I don't understand what you mean @thesayhey

thesayhey Over a year ago

I want to replace b.credit with ` var creditHours = ddObjectArray[eeIndex].creditHours;` but the console is complaining creditHours is not defined

baao Over a year ago

There's no point of doing this. Replace b.credit with b.creditHours ... @thesayhey

thesayhey Over a year ago

shouldn't the console.log spit out creditHours as well ? and the json object be creditHours too?

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