在setTimeout（）中将参数传递给匿名函数

Question

I am trying to figure out why the following code does not work

function testFunction(fn) {
    setTimeout(fn(1), 1000)
}

this.testFunction(id => console.log("id; " + id))

Removing setTimeout() and simply using fn(1) will console log the desired result

id; 1

Answer 1

Your function accepts an argument and as a consequence it is immediately invoked. Put the algorithm in an anonymous function.

setTimeout(() => fn(1), 1000)

Answer 2

As Jaromanda X points out in the comments, any parameters that need to be passed to the anonymous function must be passed to the setTimeout function rather than using brackets notation - fn(1) - as that invokes the anonymous function before it is passed to setTimout

function testFunction(fn) {
    setTimeout(fn, 1000, 1)
}