What is the reason that when a variable is embedded within another variable, its value remains anchored to its initial declaration?

Question

What is the reason that when a variable is embedded within another variable, its value remains anchored to its initial declaration?

When looking at the code below, one would anticipate the output to read "text something different" but instead it displays "text something".

var dynamic = "something";

var thistext = "text " + dynamic;

dynamic = "something different";

console.log(thistext);

The value assigned to the variable "dynamic" is changed after assigning it to the variable "thistext." Nevertheless, this alteration does not impact the value of "dynamic" within "thistext."

While this may seem like a basic concept, I appear to be unfamiliar with this rule or how best to address this issue.

To see the code in action, visit this Jsfiddle:

https://jsfiddle.net/k5wwpvgt/

javascript

Answer 1

Answer №1

How come a variable's value is fixed to the first declaration when used within another variable?

When you use a variable in an expression, the result of that expression is assigned to another variable. Expressions are evaluated based on the current values of the variables they contain. This behavior is fundamental in JavaScript and other imperative/procedural languages.

Expressions do not dynamically update when their inputs change, nor do variables automatically update themselves based on past assignments. If you want a calculation to be redone when its inputs change, create a function and call it as needed. Functions are dynamic definitions of calculations that can be updated by changing their inputs.

Is there a way to reference a variable within another variable without capturing the value at assignment?

A variable simply holds a value and does not retain information about how or when it was assigned. It cannot store a reference to another variable. Variables are like boxes that hold values, without any built-in mechanism for self-updating or referencing other variables directly.

What is the best approach to handle this situation?

This behavior is intrinsic to JavaScript and not something to avoid. Understand how variables and expressions work to effectively manage your code.

Answer 2

How come a variable's value is fixed to the first declaration when used within another variable?

When you use a variable in an expression, the result of that expression is assigned to another variable. Expressions are evaluated based on the current values of the variables they contain. This behavior is fundamental in JavaScript and other imperative/procedural languages.

Expressions do not dynamically update when their inputs change, nor do variables automatically update themselves based on past assignments. If you want a calculation to be redone when its inputs change, create a function and call it as needed. Functions are dynamic definitions of calculations that can be updated by changing their inputs.

Is there a way to reference a variable within another variable without capturing the value at assignment?

A variable simply holds a value and does not retain information about how or when it was assigned. It cannot store a reference to another variable. Variables are like boxes that hold values, without any built-in mechanism for self-updating or referencing other variables directly.

What is the best approach to handle this situation?

This behavior is intrinsic to JavaScript and not something to avoid. Understand how variables and expressions work to effectively manage your code.

Answer 3

Answer №2

It is true that, as pointed out by others, this behavior is to be expected; to achieve your desired outcome, you can utilize a function:

let dynamic = "something";
let generateText = () => "text " + dynamic;
dynamic = "something different";
console.log(generateText());

Note the distinctions! Now 'generateText' is a function that needs to be invoked with (), and it will be reevaluated each time.

Answer 4

It is true that, as pointed out by others, this behavior is to be expected; to achieve your desired outcome, you can utilize a function:

let dynamic = "something";
let generateText = () => "text " + dynamic;
dynamic = "something different";
console.log(generateText());

Note the distinctions! Now 'generateText' is a function that needs to be invoked with (), and it will be reevaluated each time.

Answer 5

Answer №3

thistext doesn't have the variable dynamic, but it includes the actual values of that variable when the expression was calculated.

Answer 6

thistext doesn't have the variable dynamic, but it includes the actual values of that variable when the expression was calculated.

Answer 7

Answer №4

Once your JavaScript code is compiled by the browser, it will resemble something like this:

var dynamic = undefined;
 var thisText = undefined;

dynamic = "something";

thistext = "text " + dynamic;

dynamic = "something different";

console.log(thistext);

When you log the value, you are only logging the value of thisText, which is set when dynamic has a value of "something".

If you perform the same operation after changing the value of dynamic, you will see the desired result.

I hope this explanation clears things up for you.

Answer 8

Once your JavaScript code is compiled by the browser, it will resemble something like this:

var dynamic = undefined;
 var thisText = undefined;

dynamic = "something";

thistext = "text " + dynamic;

dynamic = "something different";

console.log(thistext);

When you log the value, you are only logging the value of thisText, which is set when dynamic has a value of "something".

If you perform the same operation after changing the value of dynamic, you will see the desired result.

I hope this explanation clears things up for you.

What is the reason that when a variable is embedded within another variable, its value remains anchored to its initial declaration?

Answer №1

Answer №2

Answer №3

Answer №4

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