arrow-functions

问题 const makeIncrementer = s=>a=>a+s makeIncrementer(10).toString() // Prints 'a=>a+s' which would make it impossible to de-serialize correctly (I would expect something like a=>a+10 instead. Is there a way to do it right? 回答1: This is a great question. While I don't have a perfect answer, one way you could get details about the argument/s is to create a builder function that stores the necessary details for you. Unfortunately I can't figure out a way to know which internal variables relate to

问题 I've heard that passing an arrow function as a prop is not ideal because it creates a new function every time which will lead to performance issues. However, I'm not entirely sure how to completely move away from them, as can be seen by the example below: class Home extends Component { onCardPress = (message) =>{ alert(message) } render(){ return( <View> <Card onCardPress={this.onCardPress} message="Hello world!" /> </View> ) } } class Card extends Component { render(){ const { onCardPress ,

问题 I see this a lot in ES6 React code class Foo extends React.Component { bar = () => { console.log("bar") } baz() { console.log("baz") } } Seems like they both define methods bar and baz on Foo but how are they different. 回答1: The declarations differ in how the function are written and the context of this , In the first syntax bar = () => { console.log("bar") } the function is written using Arrow function syntax. An arrow function does not have its own this ; the this value of the enclosing

问题 For example in redux actions, I've seen in someone's code: export const updateMessage = text => { return (dispatch) => { dispatch(updateChatMessage(text)) } } and: const updateChatMessage = text => ({ type: types.someActionType, text }) it seems to function as an imply a return but I thought that was already implied in an arrow functions brackets following the fat arrow. What do the parenthesis ({...}) do? are they necessary? Is there an alternate way to accomplish the same thing? 回答1: when

问题 I'm trying to configure webpack (5) with babel, using babel-loader to transpile to ES5. Unfortunately, the output is not consistent. Basically, it's divided into two parts: Some polyfills: My code: As you can see, the first part contains arrow functions, and the second one not. I've tried to add @babel/plugin-proposal-class-properties and @babel/plugin-transform-arrow-functions to my .babelrc file, but the class-properties is missing (with debug enabled). I must admit, I'm not sure that the

问题 I'm trying to configure webpack (5) with babel, using babel-loader to transpile to ES5. Unfortunately, the output is not consistent. Basically, it's divided into two parts: Some polyfills: My code: As you can see, the first part contains arrow functions, and the second one not. I've tried to add @babel/plugin-proposal-class-properties and @babel/plugin-transform-arrow-functions to my .babelrc file, but the class-properties is missing (with debug enabled). I must admit, I'm not sure that the

来源： https://stackoverflow.com/questions/45299584/javascript-old-syntax-to-arrow-function-conversion

来源： https://stackoverflow.com/questions/45299584/javascript-old-syntax-to-arrow-function-conversion

问题 I’m getting the error “Uncaught SyntaxError: Unexpected token => ” on my console when I put the e parameter in parentheses and then use an ES6 arrow function. However, there’s no error when I remove the parameter from the parentheses. Should the parameter not have parentheses? document.querySelector("#book-form").addEventListener("submit", (e) => { // … }); 回答1: Arrow functions cannot have a newline between the parameters and the => : 14.2 Arrow Function Definitions ArrowFunction[In, Yield,

问题 I'm using arrow functions in an app and sometimes there is the need to get a reference to the function itself. For normal javascript functions, I can just name them and use the name from within. For arrow functions, I'm currently using arguments.callee . Is there a way to name arrow functions so that a reference can be used from within? Sample code //typescript private evaluateIf(expr: parserModule.IIfExpression, callback: IEnvCallback) { this.evaluate(expr.condition, proceed=> { guard