JavaScript: Update the object's style.left property by modifying the value of x

Question

JavaScript: Update the object's style.left property by modifying the value of x

My current scenario is as follows:

I have a div with a CSS property of `left:10px;`. All div elements have their positions set to fixed. I store this value in a variable using JavaScript:

var Left = document.getElementById("div").style.left;

By alerting the variable Left, I receive a message displaying "10px". You can view this example on JSFiddle here: http://jsfiddle.net/L19rq2tk/2/

Now, my goal is to update the position value using the variable Left. I have tried various approaches, but none seem to work:

Left = "100px"; --> does not work
Left = 100px;   --> does not work
Left = "100";   --> does not work
Left = 100;     --> does not work

Fortunately, I found that I can successfully change the position by directly targeting the element:

document.getElementById("div").style.left = "100px";

If anyone has any advice or solutions to this dilemma, it would be greatly appreciated!

javascript html css position

Answer 1

Answer №1

left is compatible with position:absolute
Check out the latest fiddle here
Newly Revised

When you add position, whether it's relative or absolute, it will get the job done. Adding position:absoute could potentially have some negative effects on your design(as mentioned by Ionic in the comment)
See the demonstration

Answer 2

left is compatible with position:absolute
Check out the latest fiddle here
Newly Revised

When you add position, whether it's relative or absolute, it will get the job done. Adding position:absoute could potentially have some negative effects on your design(as mentioned by Ionic in the comment)
See the demonstration

Answer 3

Answer №2

To effectively implement the explicit form you mentioned in your response, utilize

document.getElementById("div").style.left = "100px";

. If your goal is to optimize performance by minimizing element lookups, consider employing the following approach:

var savedStyle = document.getElementById("div").style;
savedStyle.left = '100px';

The reason why the method you are attempting doesn't work as expected is that Left creates a new copy of the value instead of referencing the existing one. Modifying the Left property only alters the stored value, not the original value that object.style.left holds. Although multiple variables can point to the same object, they cannot point to the same value simultaneously. You can observe this concept with an illustrative snippet demonstrating the distinction.

var x = 1;
var y = x;
document.write('x = ' + x + '<br>');
document.write('y = ' + y + '<br>');
document.write('Updating y to 2<br>');
y = 2;
document.write('x now equals = ' + x + '<br>');
document.write('y now equals = ' + y + '<br>');

var xObj = { myValue: 3 };
var yObj = xObj;
document.write('xObj.myValue = ' + xObj.myValue + '<br>');
document.write('yObj.myValue = ' + yObj.myValue + '<br>');
document.write('Changing yObj.myValue to 1<br>');
yObj.myValue = 1;
document.write('xObj.myValue is now = ' + xObj.myValue + '<br>');
document.write('yObj.myValue is now = ' + yObj.myValue + '<br>');

Answer 4

To effectively implement the explicit form you mentioned in your response, utilize

document.getElementById("div").style.left = "100px";

. If your goal is to optimize performance by minimizing element lookups, consider employing the following approach:

var savedStyle = document.getElementById("div").style;
savedStyle.left = '100px';

The reason why the method you are attempting doesn't work as expected is that Left creates a new copy of the value instead of referencing the existing one. Modifying the Left property only alters the stored value, not the original value that object.style.left holds. Although multiple variables can point to the same object, they cannot point to the same value simultaneously. You can observe this concept with an illustrative snippet demonstrating the distinction.

var x = 1;
var y = x;
document.write('x = ' + x + '<br>');
document.write('y = ' + y + '<br>');
document.write('Updating y to 2<br>');
y = 2;
document.write('x now equals = ' + x + '<br>');
document.write('y now equals = ' + y + '<br>');

var xObj = { myValue: 3 };
var yObj = xObj;
document.write('xObj.myValue = ' + xObj.myValue + '<br>');
document.write('yObj.myValue = ' + yObj.myValue + '<br>');
document.write('Changing yObj.myValue to 1<br>');
yObj.myValue = 1;
document.write('xObj.myValue is now = ' + xObj.myValue + '<br>');
document.write('yObj.myValue is now = ' + yObj.myValue + '<br>');

Answer 5

Answer №3

Check out this code example.

You set the size to 100px, but forgot to include position:relative or position:absolute. As a result, nothing is visible on the screen because it's being placed in the background.

Answer 6

Check out this code example.

You set the size to 100px, but forgot to include position:relative or position:absolute. As a result, nothing is visible on the screen because it's being placed in the background.

Answer 7

Answer №4

By setting the value to the variable left, nothing will happen. You must assign the value to the HTML element.

Try this:

document.getElementById("div").style.left="100px";

"left" is a variable that only retains the previous value.

Additionally, you need to specify

position: relative

for your div so it can move. The left, top, and other position CSS properties can only take effect if the element has a position property, which was missing in yours.

http://jsfiddle.net/L19rq2tk/

Here is the updated fiddle for you;

Answer 8

By setting the value to the variable left, nothing will happen. You must assign the value to the HTML element.

Try this:

document.getElementById("div").style.left="100px";

"left" is a variable that only retains the previous value.

Additionally, you need to specify

position: relative

for your div so it can move. The left, top, and other position CSS properties can only take effect if the element has a position property, which was missing in yours.

http://jsfiddle.net/L19rq2tk/

Here is the updated fiddle for you;

JavaScript: Update the object's style.left property by modifying the value of x

Answer №1

Answer №2

Answer №3

Answer №4

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