How to use JavaScript Promise
Today, I would like to share with you the relevant knowledge of how to use JavaScript Promise. The content is detailed and the logic is clear. I believe most people still know too much about this knowledge, so share this article for your reference. I hope you can get something after reading this article. Let's take a look at it.
Let's describe the use of Promise by dissecting this Promise "timer" code:
The Promise constructor has only one argument, which is a function, which will be run asynchronously after it is constructed, so we call it the starting function. The starting function takes two parameters, resolve and reject.
When Promise is constructed, the initiating function is executed asynchronously:
Case study
New Promise (function (resolve, reject) {
Console.log ("Run")
})
This program will output Run directly.
Both resolve and reject are functions, where calling resolve means everything is normal, and reject is called when an exception occurs:
Case study
New Promise (function (resolve, reject) {
Var a = 0
Var b = 1
If (b = = 0) reject ("Divide zero")
Else resolve (a / b)
}) .then (function (value) {
Console.log ("a / b =" + value)
}) .catch (function (err) {
Console.log (err)
}) .finally (function () {
Console.log ("End")
})
The execution result of this program is:
A / b = 0
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