Javascript: How to display next array value on button click

Question

I am trying to write a code in javascript/jquery and html which I thought would be fairly simple, but turns out to be quite challenging (to me). I have a program which computes the first x numbers of the fibonacci sequence, and stores it in an array. What I am trying to do is make two buttons that will display the next or previous number in the sequence. This is what I have so far.

Javascript:

var all = new Array();
fib = function (numMax) {
    for (i = 0, j = 1, k = 0; k < numMax; i = j, j = x, k++) {
        x = i + j;
        //window.document.write(x + " ");
        all[k] = x;
    }
};

fib(1000);

fibon = function () {
    getElementById("mynum").innerHTML = "all[+1]";
};

HTML:

<input type="text" id="mynum">
<button onclick="fibon();">Next</button>

Barmar · Accepted Answer · 2014-10-03 21:57:03Z

5

You need a variable that contains the current index, and then increment it each time you click.

fibindex = 0;

function fibon() {
    if (fibindex >= all.count) {
        document.getElementById("mynum").value = "We've run out of Fibonacci numbers";
    } else {
        document.getElementById("mynum").value = all[fibindex];
        fibindex++;
    }
}

Also, notice that you should not put quotes around a use of a variable. Add you use .value to fill in an input, not .innerHTML.

DEMO

edited Oct 3, 2014 at 21:57

answered Oct 3, 2014 at 21:26

Barmar

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6 Comments

Barmar Over a year ago

Was just about to add that when you wrote.

VampireTooth Over a year ago

Could you make a jsfiddle please?

VampireTooth Over a year ago

How would I add a button to display the previous number?

Barmar Over a year ago

Exactly the same, except you decrement the index instead of incrementing it.

Barmar Over a year ago

And use 0 as the bound test, instead of all.count, of course.

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