Nested JavaScript function expression

In this JavaScript example, the snippet provided is for educational purposes and does not include validation. After defining the variable 'isBetween' within the buildBoundDetector() function, it raises questions about how passing a number through variable 'f' works in the code.

function buildBoundDetector( lowerBound, upperBound ) {
    var isBetween = function(number){       
        if(lowerBound <= number && number <= upperBound){
            return true;
        }
        return false;
    }
    return isBetween;
}

var f = buildBoundDetector( 1, 100 );
f(45);

Answer №1

generateConstraintChecker() is a JavaScript function that produces another function as its output. This concept allows functions to be assigned to variables in JavaScript, which is precisely what generateConstraintChecker() accomplishes. The process involves defining an anonymous function within the scope of generateConstraintChecker(), then assigning this function to a variable called checkConstraint. Finally, the function generateConstraintChecker() returns the reference to checkConstraint. In essence, the result of generateConstraintChecker() is a callable function stored in the variable f. By calling f, you are invoking the functionality encapsulated within the generated function.

Answer №2

One of the key features in JavaScript, as well as other programming languages, is the ability to treat functions as values. This means that a function can be returned as a value, which can then be passed on and executed like any other function. In this example, the initial function returns a reference to another function, which can then be used with an argument such as 45.

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