react

react中class组件事件处理函数中的this指向

在class组件中我们触发事件,比如点击事件后想拿到state,第一反应肯定是点击后用this.state拿数据

但是,很遗憾react中这样是拿不到的,直接报错,打印this竟然是undefined

react官方:
在JSX回调中你必须注意 this 的指向。 在 JavaScript 中,类方法默认没有绑定的。如果你忘记绑定 this.handleClick 并将其传递给onClick,那么在直接调用该函数时,this 会是 undefined 。

解决的方法

我这里列举常见的两种解决的方法,一种是用bind方法解决,一种是箭头函数;而bind方法写法有两种方案。

bind—直接在事件赋值的函数处绑定this

用bind方法为事件处理函数绑定this指向

bind—在构造函数处将bind后的返回值再次赋值给事件处理函数

箭头函数

这种写法个人还是比较喜欢的,它是点击后执行一个箭头函数(而箭头函数是不会绑定this的),再在箭头函数里执行事件处理函数并且传递参数也很方便。

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