How to check the type of a variable in JavaScript
Łukasz Holeczek
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Checking variable types is essential for writing robust JavaScript code that handles different data types safely and predictably.
As the creator of CoreUI with over 25 years of JavaScript development experience, I’ve implemented countless type checks for component validation and data processing.
From my expertise, the most reliable approach is using the typeof operator for primitive types and additional checks for arrays and null values.
This combination provides comprehensive type detection for all JavaScript data types.
Use the typeof operator to check primitive types and combine with additional checks for complex types.
function getType(value) {
if (value === null) return 'null'
if (Array.isArray(value)) return 'array'
return typeof value
}
Here typeof value returns the type as a string for most primitive types like ‘string’, ’number’, ‘boolean’, ‘undefined’, ‘function’, and ‘object’. The function handles special cases: value === null checks for null (since typeof null returns ‘object’), and Array.isArray(value) specifically identifies arrays. This approach correctly distinguishes between all JavaScript types including the edge cases that typeof alone cannot handle.
Best Practice Note:
This is the same approach we use in CoreUI components for prop validation and ensuring type safety in component interfaces. Remember that typeof has limitations - it returns ‘object’ for arrays, null, and dates, so additional checks are necessary for precise type detection.
