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The JavaScript Interview Handbook: 100+ Interview Questions

Solution Review: Asynchronous Callback Functions

Explore how asynchronous callback functions work in JavaScript to handle delayed operations like setTimeout. Understand solving timing-related errors by passing callback functions, enabling code execution after data retrieval is complete.

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Solution

Javascript (babel-node)
const getTodo = callback => {
    setTimeout(() => {
       callback ({ text: 'Complete Code Example' })
    }, 2000)
}
function display(){
getTodo(todo => {
    console.log(todo.text)
})
}
display()

Explanation

Before we discuss the solution above, let’s discuss what the original code was doing.

Javascript (babel-node)
const getTodo = () => {
    setTimeout(() => {
        return { text: 'Complete Code Example' }
    }, 2000)
}
function display(){
    const todo = getTodo()
    console.log(todo.text)
}
display()

The getTodo function has the setTimeout function which returns the object {text : 'Complete Code Example'} after two seconds pass.

In the display function, we call the getTodo ...