Add all array values before specific array value with Javascript

Question

Within my software, I have a spread viewer which aligns pages next to each other. The number of pages can vary. Users can place notes on these pages. I want to be able to tell which page the note is being added to by comparing the x coordinate to the sum of the page widths.

For this example, let's say I have a 4 page spread. I build a js array widthArr[] which has these values: [297, 300, 305, 410]

So of course to following is true

widthArr[0] = 297 //page 1 width
widthArr[1] = 300 //page 2 width
widthArr[2] = 305 //page 3 width
widthArr[3] = 410 //page 4 width

So if the x coordinate is 400, then I will know that the note is being placed on Page 2.

Is there a way that I can dynamically loop through these pages and somehow check if x is greater than the width of all previous page widths?

I would need to check the following in this particular scenario:

Is x > (widthArr[0] + widthArr[1] + widthArr[2])? Then the user is adding a note to page 4.

Is x > (widthArr[0] + widthArr[1])? Then the user is adding a note to page 3.

Is x > widthArr[0]? Then the user is adding a note to page 2. If not, then the user is adding a note to page 1.

I was starting out with the following for loop.

var spreadPagesLength = 4;
var x = 400;
var i;
for (i = 0; i < spreadPagesLength; ++i) {

}

Any help is appreciated. Thanks so much.

This sounds like an X-Y problem. How do these pages get created or widths set? Surely can add identifiers to them at that point? — charlietfl
– charlietfl, Commented Aug 25, 2015 at 15:45

Paul Roub · Accepted Answer · 2015-08-25 15:45:00Z

2

Keep a running total of widths you've seen so far, and break when the width exceeds x:

var widthArr = [297, 300, 305, 410];
var page = widthArr.length + 1;   // after the last page, as a default
var x = 400;
var totalWidth = 0;

for ( var i = 0; i < widthArr.length; ++i )
{
  totalWidth += widthArr[i];

  if (x < totalWidth)
  {
    page = i + 1;
    break;
  }
}

answered Aug 25, 2015 at 15:45

Paul Roub

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