Let's talk about Coercion today. Simply put, coercion is the process of changing a value from one type to another. Let's see a very simple example.
const number = 42
const string = String(number)
We're talking about explicit coercion in this example. We explicitly tell JavaScript to coerce a number into a string. The same is possible for other values. Let's see some more examples of explicit coercion.
const num = Number("10")
const bool = Boolean(0)
const float = parseFloat("10.2")
const anotherNum = parseInt("19")
const string = String(99)
But there are also cases (actually a lot of them) where implicit coercion will happen in JS.
const arr = []
if(arr.length){
// do something
}
You've probably written some code like this before. In this case, implicit coercion happens in the if statement, because the if statement takes a boolean as an argument and arr.length returns a number.
Another example of implicit coercion is, for example, when you use a number in a string literal like this:
const num = 42
const str = `${num} pizzas for our office, please`
In the string literal, num is implicitly coerced into a string. Of course, we could also do this explicitly:
const num = 42
const str = `${String(num)} pizzas for our office, please`
Also, coercion always happens, when you use a double equal to compare two values. It doesn't happen, when you use the triple equal:
console.log("42" == 42) // true
console.log("42" === 42) // false
In the "42" == 42 case, implicit coercion is done by JS, to compare equal types. That's why the comparison is true. The triple equal === does no implicit coercion, that's why this comparison is false.
Want to get better at Web Development?
🚀🚀🚀subscribe to the Tutorial Tuesday ✉️newsletter
Top comments (7)
NaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNNaNBatman
Batman
Array(16).join("foo" -1)+ " BATMAN"
source is still destroyallsoftware.com/talks/wat
That talk is so good!
Great article! I believe explicit type conversion is usually referred as casting, implicit type conversion would be coercion.
Great summary, Benjamin. 👏
I'd like to suggest an edit:
This statement isn't entirely accurate: double-equal will only do coercion if it the types are different; if they are the same, it delegates the comparison to triple-equal.
Good!