What's the Fastest Way to Check if a Variable is an Array in JavaScript?

Checking for Array Type in JavaScript

In JavaScript, it is crucial to determine whether a variable holds an array. Essential methods for this task include:

Fastest Method: Constructor Property

variable.constructor === Array

This method leverages the fact that JavaScript arrays inherently inherit from the Array constructor.

Checking for Array Property Attributes

variable.prop && variable.prop.constructor === Array

If dealing with nested array properties, check their existence before verifying their array type using the constructor property.

Additional Methods

• Array.isArray(variable): A concise and reliable method, however, it may exhibit slight performance disadvantages in older browsers.
• variable instanceof Array: A more verbose but flexible approach, though slightly slower than the constructor method.
• Object.prototype.toString.call(variable) === '[object Array]': A comprehensive method for checking the type of any variable. However, due to its slow performance, it is not recommended for specific array type checks.

Benchmarking Results

Benchmarks reveal that the constructor property method is the fastest and most efficient for determining array types. Array.isArray() follows closely, while instanceof Array() and toString() methods offer decent performance but fall short of the speed of the constructor property method.

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