destructuring

问题 I came across this destructuring expression in an article. const words = ['oops', 'gasp', 'shout', 'sun']; let { length } = words; console.log(length); // 4 How does length get the value of 4? I know .length is a property of the array, but how does this syntax work? It seems to be doing let length = words.length; and in fact in babel does output it as such. But my question is what is the logic behind it? What is confusing me is the mix of an array of values and the the use of {length} . I

问题 I'm pretty new to JS and i'm trying to learn some basics in functions. I'm facing a problem, I've created a function like this: function someName (element, settings={i:"#1d252c", i2:"#fff"}) { ....... } If i call the function as someName(element) . i and i2 retain their values, however If i call it like someName(element,{i:"#3acbda"}) , the value of i does change however the value of i2 is undefined, So how do i assign the default value to a property when the settings object is no longer the

问题 Is it possible to destruct the properties of an object while keeping the object as a parameter inside an array.map() function? Based on this question I tried the following but failed (parsing error) this.state.files.map(((file, {param1, param2} = file), i) => ( <div key={i}> <p>{param1}</p> <button onClick={this.editFile(file)} /> </div> ) 回答1: Instead of using lambda component make it a functional block like so this.state.files.map(((file, i) => { const {param1, param2} = file; return ( <div

问题 According to this source and a vague memory of having seen this sort of usage in a project somewhere, I'm curious if anyone has been able to do the following: import {map: { series }} from 'contra' As stated on this destructuring assignment overview: The import statement in ES6 behaves similarly to destructuring, but it is important to note that it is not actually destructuring. It appears that imports work a little different and perhaps one cannot expect the same exact behavior, but I haven

问题 Here is the code in question: const posts = [{ data: { id: 1, date: "2019-02-03", ev_filter_1: ["art", "foodie"], ev_filter_2: ["value1", "value2"], ev_filter_3: ["value1", "value2"], ev_filter_4: ["all", "12+"] } }, { data: { id: 2, date: "", ev_filter_1: ["arti", "foodie"], ev_filter_2: ["value1", "value2"], ev_filter_3: ["value1", "value2"], ev_filter_4: ["all", "19+"] } }, { data: { id: 3, date: "2019-02-03", ev_filter_1: ["art", "foodie"], ev_filter_2: ["value1", "value75"], ev_filter_3:

问题 It's pretty simple: Object.entries is supposed to produce and Array of key, value pairs.. As such, I would expected this code to destructure [{ id: 1, name: "christian" },{ id : 2, name: "bongiorno" }].map(Object.entries).forEach(([k,v]) => console.log(`${k}: ${v}`)); into producing: id:1 name:christian id:2 name:bongiorno But it doesn't. I get, instead: id,1: name,christian id,2: name,bongiorno What did I miss? 回答1: The output is correct but your definition is slightly off, you're missing an

问题 I have code of the shape (let [{foo :foo} (make-foo)] ...) This code occasionally emits a java.lang.IllegalArgumentException: No value supplied for key: {:foo "foo" :other "other"} . I've seen Clojure : "java.lang.IllegalArgumentException: No value supplied for key:" when I changed require, however I haven't changed the require of my program since it last worked. What are the possible causes for the "No value supplied for key" exception? 回答1: This happens when you try to create a map from an

问题 I have an object { hello_en: 'hello world', 'hello_zh-CN': '世界您好', something: 'nice day', something_else: 'isn\'t it' } being passed into a function function(data) { const { hello_en, hello_zh-CN, ...rest } = data // do some stuff with hello_en and hello_zh-CN // so some other stuff with rest } but of course hello_zh-CN is not a valid key name. I am unable to write const { hello_en, 'hello_zh-CN', ...rest } = data as that gives an error. How can I destructure an object's properties when one

问题 This question already has answers here : Object destructuring with property names that are not valid variable names (2 answers) Closed 3 years ago . How do I destructure a property from an object where the key contains a hyphen? Eg: { accept-ranges:"bytes", cache-control:"public, max-age=0", content-length:"1174", content-type:"application/json", date:"Mon, 03 Oct 2016 06:45:03 GMT", etag:"W/"496-157892e555b"", last-modified:"Mon, 03 Oct 2016 06:14:57 GMT", x-powered-by:"Express" } Now to get

问题 Say I have an object foo with properties a and b but I want to transfer the values of these properties to another object bar with properties x and y where bar.x gets the value of foo.a and bar.y gets the value of foo.b . The first way that comes to mind to accomplish this with ES5 would be like the following. var foo = { a: 5, b: 17 }; var bar = { x: foo.a, y: foo.b }; This is already pretty terse but having to reference foo in each case to access it's properties gets noisy for a larger