How to Set an Object Key by Variable in JavaScript

To set an object key by variable in JavaScript, you can use either “dot notation” or “square bracket” notation.

Here’s an example using both notations:

const mainObj = {};
const key = 'mainKey';
const value = 'mainValue';

// Using dot notation
mainObj[key] = value;

// Using square bracket notation
mainObj.key2 = 'mainValue2';



{ mainKey: 'mainValue', key2: 'mainValue2' }

In this code example, we created a new empty object mainObj.

A variable key is assigned the string value ‘mainKey‘, and a variable value is assigned the string value ‘mainValue’.

The key variable is used to set the value of a property on ‘mainObj’ using square bracket notation (mainObj[key] = value), which dynamically sets the object key based on the value of the key.

Another key2 is set using dot notation (mainObj.key2 = ‘mainValue2’), which sets the object key to the literal string ‘key2’.

Finally, the mainObj object is logged into the console.

The dot notation only works if the key name is a valid identifier, which means it must start with a letter, underscore, or dollar sign and may contain letters, digits, underscores, or dollar signs.

You must use square bracket notation if the key name is not a valid identifier. Square bracket notation is also required to use a variable to set the key name dynamically.

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