Please explain this line of js code.

Question

I have the following javascript code block, and is not very clear about it:

var level = this.getLevelForResolution(this.map.getResolution());
var coef = 360 / Math.pow(2, level);

var x_num = this.topTileFromX < this.topTileToX ? Math.round((bounds.left - this.topTileFromX) / coef) : Math.round((this.topTileFromX - bounds.right) / coef);
var y_num = this.topTileFromY < this.topTileToY ? Math.round((bounds.bottom - this.topTileFromY) / coef) : Math.round((this.topTileFromY - bounds.top) / coef);

What does the < in this.topTileFromX < mean?

"<" is the less than sign in the condition of a ternary operator. Beyond that, the question isn't very clear. — Tim M.
– Tim M., Commented Mar 8, 2013 at 6:15
@TimMedora, I think he has difficulties in expressing in English. I have edited the question to make it more clear. — saji89
– saji89, Commented Mar 8, 2013 at 6:29

Bondt · Accepted Answer · 2015-06-10 15:47:11Z

1

That's a JavaScript Ternary operator. See Details Here

var x_num = this.topTileFromX < this.topTileToX ? Math.round((bounds.left - this.topTileFromX) / coef) : Math.round((this.topTileFromX - bounds.right) / coef);

is equivalent to the following expression

var x_num;

if (this.topTileFromX < this.topTileToX )
{
    x_num= Math.round((bounds.left - this.topTileFromX) / coef);
}
else
{
    x_num= Math.round((this.topTileFromX - bounds.right) / coef);
}

edited Jun 10, 2015 at 15:47

Bondt

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answered Mar 8, 2013 at 6:14

Hanky Panky

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Comments

Albert Xing · Accepted Answer · 2013-03-08 06:15:09Z

0

< means "lesser than", like in Mathematics.

Thus

2 < 3 returns true
2 < 2 is false
3 < 2 is also false

answered Mar 8, 2013 at 6:15

Albert Xing

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Comments

Felipe Francisco · Accepted Answer · 2013-03-08 06:17:03Z

0

var x_num = this.topTileFromX < this.topTileToX ? Math.round((bounds.left - this.topTileFromX) / coef) : Math.round((this.topTileFromX - bounds.right) / coef);

It's a shorter if statement. It means:

var x_num;

if(this.topTileFromX < this.topTileToX)
{
   x_num = Math.round((bounds.left - this.topTileFromX) / coef);
}
else
{
   x_num = Math.round((this.topTileFromX - bounds.right) / coef);
}

answered Mar 8, 2013 at 6:17

Felipe Francisco

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