Attention should be paid to the first parameter of setTimeout

setTimeout The first parameter should pay attention to

The first parameter should be a function , Instead of a function call .

setTimeout(console.log('2333'), 1000)

Such a statement seems to have no problem ,1000 In milliseconds console.log(‘23333’). But it's totally wrong , In the browser you will find , He didn't wait 1000 millisecond , And directly output .

And in the node Will be output immediately 23333 Report a mistake later .

The error message is Callback must be a function. Received undefined. We know ,console.log The return value of undefined.

therefore console.log('23333') It looks like a function here , And he is actually a undefined.

So we can have two solutions , One is to pass in parameters later .

setTimeout(console.log, 1000, '23333')

This is troublesome when there are many parameters , It's not easy to understand .

A better way is to wrap the call statement in an arrow function .

setTimeout(() => console.log('23333'), 1000)

This is beautiful and easy to understand .