Issue
I want to have a webpage whose entire viewable area is filled with divs. I am currently using the following code:
var wh= window.innerHeight;
var ww= window.innerWidth;
var area= wh * ww;
i= 1;
while(area > 0) {
document.getElementById("map").innerHTML+= "<div class='map-box' id='box" + i + "'></div>";
area-= 20 * 20;
i+=1;
}.map-box {width: 20px; height: 20px; border-color: grey; border-width: 1px; border-style: solid; display: inline-block; margin: 0; padding: 0;}<body>
<div id='map'></div>
</body>If you try to use this code is your browser, you will see that there are two flaws in this:
- First, it creates too many extra divs which go outside the viewable screen.
- Second, this code is also somewhat slow.
Can someone here help me address both of these flaws and also optimize this code for faster performance?
Solution
Instead of accessing dom element's inner html on each loop iteration - do it once after the loop with "prepared" data to set there
const wh = window.innerHeight;
const ww = window.innerWidth;
let area = wh * ww;
i = 1;
const ms = Date.now();
const divs = [];
while (area > 0) {
divs.push("<div class='map-box' id='box" + i + "'></div>");
area -= 20 * 20;
i += 1;
}
document.getElementById("map").innerHTML = divs.join("");
console.log("done fast", Date.now() - ms);
js fiddle with comparison https://jsfiddle.net/aL7zqwy9/
The final solution, not ideal but
<html>
<body>
<div id='map'></div>
</body>
<style>
body {
margin: 0;
padding: 0;
/* Overflow appears when last row is added and shrinks the "width" */
overflow-y: hidden;
}
#map {
/* To exclude space between rows */
display: flex;
flex-direction: row;
flex-wrap: wrap;
}
.map-box {
width: 20px;
height: 20px;
border: 1px solid grey;
display: block;
margin: 0;
padding: 0;
/* So border thickness will not affect element size */
box-sizing: border-box;
}
</style>
<script>
const cellSize = 20; // px
const wh = window.innerHeight;
const ww = window.innerWidth;
// not always divisible by cell size without a remainder
const columnsCount = Math.floor(ww / cellSize);
const rowsCount = Math.floor(wh / cellSize);
const cellsCount = columnsCount * rowsCount;
console.log(`wh: ${wh}, ww: ${ww}, cols: ${columnsCount}, rows: ${rowsCount}`);
const divs = [];
for (let i = 0; i < cellsCount; i++) {
divs.push(`<div class='map-box' id='box${i}'></div>`);
}
document.getElementById("map").innerHTML = divs.join("");
</script>
</html>
Answered By - Sergey Sosunov
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