One of the easiest ways we can use JavaScript to check if a variable is a function is by using the JavaScript typeof Operator in an if conditional statement.
if ( typeof someVariable == "function" ){
//The variable IS a function
}
In the code above, someVariable is the variable that we want to check to see if it is a function. typeof someVariable will return “function” if the variable is a function, and therefore the conditional statement will be true.
We can put this code in a function to make checking if a variable is a function very simple.
Here is the function:
function isFunction(variable){
if ( typeof variable == "function" ){
return true;
} else {
return false;
}
};
Our function simply returns true if the variable you enter is a function, and false if not.
Now let’s show some examples of this function is use:
function isFunction(variable){
if ( typeof variable == "function" ){
return true;
} else {
return false;
}
};
var variable1 = {name:'tom', age:25};
var variable2 = [1,2,3,4];
var variable3 = "1234";
var variable4 = ["Red","Yellow","Green","Blue"];
var variable5 = function isFunction(variable){
if ( typeof variable == "function" ){
return true;
} else {
return false;
}
};
var variable6 = {};
console.log(isFunction(variable1));
console.log(isFunction(variable2));
console.log(isFunction(variable3));
console.log(isFunction(variable4));
console.log(isFunction(variable5));
console.log(isFunction(variable6));
#Output:
false
false
false
false
true
false
Hopefully this article has been useful for you to learn how to use JavaScript to check if a variable is a function.