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Get global variable dynamically by name string in JavaScript?

Javascript Web Development Object Oriented Programming

In JavaScript, you can access global variables dynamically using their name as a string through the window object (in browsers) or global object (in Node.js).

Syntax

// Browser environment
window[variableName]

// Node.js environment  
global[variableName]

// Using globalThis (works in both)
globalThis[variableName]

Basic Example

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Dynamic Global Variables</title>
</head>
<body>
    <script>
        // Define global variables
        var userName = "John";
        var userAge = 25;
        var userCity = "New York";
        
        // Access using string names
        console.log(window["userName"]);   // John
        console.log(window["userAge"]);    // 25
        console.log(window["userCity"]);   // New York
        
        // Dynamic access with concatenated strings
        var prefix = "user";
        console.log(window[prefix + "Name"]);  // John
        console.log(window[prefix + "Age"]);   // 25
    </script>
</body>
</html>

John
25
New York
John
25

Dynamic Variable Construction

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Dynamic Variable Names</title>
</head>
<body>
    <script>
        // Global variables with pattern
        var globalVariablelocal_print100 = 100;
        var globalVariablelocal_print200 = 200;
        var print100 = 1;
        var print200 = 2;
        
        // Build variable name dynamically
        var baseName = "globalVariable";
        var middlePart = "local_print";
        var suffix = "00";
        
        var dynamicVarName1 = baseName + "local_print1" + suffix;
        var dynamicVarName2 = baseName + "local_print2" + suffix;
        
        console.log("First variable:", window[dynamicVarName1]);   // 100
        console.log("Second variable:", window[dynamicVarName2]);  // 200
        
        // Using concatenation like in original example
        alert(window['globalVariable' + 'local_print1' + '00']);
    </script>
</body>
</html>

First variable: 100
Second variable: 200

Using globalThis (Modern Approach)

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>globalThis Example</title>
</head>
<body>
    <script>
        // Global variables
        var config_apiUrl = "https://api.example.com";
        var config_timeout = 5000;
        
        // Function to get config values dynamically
        function getConfig(key) {
            var varName = "config_" + key;
            return globalThis[varName];
        }
        
        console.log("API URL:", getConfig("apiUrl"));    // https://api.example.com
        console.log("Timeout:", getConfig("timeout"));   // 5000
        console.log("Missing:", getConfig("missing"));   // undefined
    </script>
</body>
</html>

API URL: https://api.example.com
Timeout: 5000
Missing: undefined

Key Points

window[variableName] works in browsers
global[variableName] works in Node.js
globalThis[variableName] works in both environments
Returns undefined if the variable doesn't exist
Only works with variables declared with var or without declaration keywords
Variables declared with let or const are not added to the global object

Conclusion

Use window[variableName] in browsers or globalThis[variableName] for cross-platform compatibility to access global variables dynamically by their string names.

AmitDiwan

Updated on: 2026-03-15T23:18:59+05:30

531 Views

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