Summary - Type conversion
Write a function that safely converts user input to numbers using type conversion.
Summary - Type conversion
In this group you saw the two faces of type conversion. With explicit conversion you use the String(), Number() and Boolean() functions. With implicit coercion, structures like +, - and if change the type for you.
You also learned the difference between == and ===, the six falsy values and the NaN trap of Number(). Now you will write a function that combines all of this: it will safely convert a user-entered string to a number and catch invalid input.
Exercise Safe toNumber function
Define a function called toNumber. It should take an input parameter. Inside, convert to a number with let n = Number(input). Check for NaN with if (Number.isNaN(n)); if it is NaN, return null. Otherwise, finally return n to give the number back.
Show example solution
function toNumber(input) {
let n = Number(input);
if (Number.isNaN(n)) {
return null;
}
return n;
}Exercise Call toNumber with four values
The toNumber function below is defined. Now call it with four values and print the result: console.log(toNumber("42")), console.log(toNumber("abc")), console.log(toNumber("")) and console.log(toNumber("0")). Put each call on its own line.
Show example solution
function toNumber(input) {
let n = Number(input);
if (Number.isNaN(n)) {
return null;
}
return n;
}
console.log(toNumber("42"));
console.log(toNumber("abc"));
console.log(toNumber(""));
console.log(toNumber("0"));Test yourself
-
Match the concepts
- String()
- Explicit
- + "5"
- Implicit
- ===
- Strict equality
- 0
- Falsy value
-
Which is an explicit type conversion?
- "5" - 0
- +"5"
- Number("5")
- "5" + 3
Show answer
Number("5") — Correct. Number("5") explicitly converts to a number; the others are implicit coercion.