JavaScript Program to Check If a Variable is of Function Type

To understand this example, you should have the knowledge of the following JavaScript programming topics:


Example 1: Using instanceof Operator

 // program to check if a variable is of function type function testVariable(variable) { if(variable instanceof Function) { console.log('The variable is of function type'); } else { console.log('The variable is not of function type'); } } const count = true; const x = function() { console.log('hello') }; testVariable(count); testVariable(x);

Output

 The variable is not of function type The variable is of function type

In the above program, the instanceof operator is used to check the type of variable.


Example 2: Using typeof Operator

 // program to check if a variable is of function type function testVariable(variable) { if(typeof variable === 'function') { console.log('The variable is of function type'); } else { console.log('The variable is not of function type'); } } const count = true; const x = function() { console.log('hello') }; testVariable(count); testVariable(x);

Output

 The variable is not of function type The variable is of function type

In the above program, the typeof operator is used with strict equal to === operator to check the type of variable.

The typeof operator gives the variable data type. === checks if the variable is equal in terms of value as well as the data type.


Example 3: Using Object.prototype.toString.call() Method

 // program to check if a variable is of function type function testVariable(variable) { if(Object.prototype.toString.call(variable) == '[object Function]') { console.log('The variable is of function type'); } else { console.log('The variable is not of function type'); } } const count = true; const x = function() { console.log('hello') }; testVariable(count); testVariable(x);

Output

 The variable is not of function type The variable is of function type 

The Object.prototype.toString.call() method returns a string that specifies the object type.


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