In alot of cases in javascript, you will find it very difficult to pass certain parameter values or context to the function call. For example, the keyword 'this' which will mean very different things each time it is used depending on the context in which it was used and how it was used, inside a function or outside it, inside a function defined with the function keyword or an arrow function. Also when triggering an event that call a function and you need to pass/bind some parameters to this function. So here is a good explanation for the bind(), call() and apply() functions.