How to solve the problem of method closure caching in methods in vue
This article mainly introduces how to solve the problem of method closure caching in methods in vue. It has certain reference value. Now I share it with you. Friends in need can refer to it
vue中Method closure caching problem in methods
Problem background
Requirement description
It is required in the navigation bar of the route to determine whether it is the first time Click
Needs a flag to record whether clicked
Current situation:
- # #This flag is only used in one function. I don’t want to store the global
- I hope to form a closure in this methods to cache this function
- After making the following attempts, we found that it can be achieved.
- Current problem:
- cannot be closed The correct this is found when the package is called.
- When tested: the returned this is found in window
// 测试使用:
<p>
<button>测试按钮</button>
</p>
<script>
var app = new Vue({
el: '#app',
methods: {
test: (() => {
`use strict`
console.log(this) // Window
var flag = true
return () => {
console.log(this) // Window
flag = false
}
})()
}
})
</script>- This in the actual project became
undefined
- ##What’s even weirder is that after
- debugger
, let’s look at the
current code step by step: -
pointJump: (() => { let isFirstChanged = false; console.log(this); debugger; return entry => { console.log(this); console.log(isFirstChanged); debugger; isFirstChanged = true; }; })(),Copy after login
- Operation:
- Refresh the page, the first function will be executed immediately
After the page generation is completed: We trigger the event through the button again: - At this time, the debugger displays the top-level object of Vue in the memory, but what is printed on the console is still undefined
Execution process analysis
- First It is normal for it to be undefined when executed for the first time, because the first time the closure was executed, this
- was not found. When we executed it again, although the calling context, that is, this has been It has been changed, but because the space represented by
- this
in the scope is still
undefined, it cannot be changed. causes The strange phenomenon we saw. - The reason why it is different from the test file
- is because in the test environment, it could not be opened Strict mode.
- After two attempts to open it at different locations, both failed.
- The window object can still be found
- It needs to be tested again, and you still need to go through it carefully to see the source code
<script> var app = new Vue({ el: '#app', methods: { test: (() => { `use strict` console.log(this) // Window var flag = true return () => { console.log(this) // Window flag = false } })() } }) </script>Copy after loginThe final test to find the reason
- Because the this of the arrow function will not change, it has this that can be returned by the parent
- Then because this in the above closure environment always points to
- undefined
##Solutionconst test = (() => { let aaa = true; return function () { console.log(this); aaa = false; }; })(); mainJump(entry) { test.call(this); },Copy after login
- In the function returned by the closure, do not use arrow functions, just use function definitions
-
Summary
pointJump: (() => { let isFirstChanged = false; return function () { console.log(this); // Vue的顶级对象 isFirstChanged = true; }; })(),Copy after login
- When returning functions in closures and caching variables, use function to define the return function.
- The above is the entire content of this article. I hope it will be helpful to everyone’s study. For more related content, please pay attention to the PHP Chinese website!
Vue2.0 custom instructions and instance properties and methods
Communication between parent and child components in Vue
The above is the detailed content of How to solve the problem of method closure caching in methods in vue. For more information, please follow other related articles on the PHP Chinese website!
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