destructuring

问题 In a let form (Clojure here) I can doing something like (let [[u s v] (svd A)] (do-something-with u v)) where svd returns a list of length three. This is a very natural sort of thing to do, so why isn't that we don't we have (def [u s v] (svd A)) and its various generalizations as the default behavior of the def form? I don't see how this would interfere with anything that def is already doing. Can someone who understands the Zen of Lisp or Clojure explain why def does not support binding

问题 How can I extract the specific column from an object, I have a column array and I want these fields extracted from an object which will be constructed by map loop function which is the item. Now here, how can check my fields dynamically. i don't want item[col[0]] like this. please tell me a short cut. const person = [{ firstName: "Nick", lastName: "Anderson", age: 35, sex: "M" }, { firstName: "yopm", lastName: "Geyun", age: 36, sex: "M" }] const col=['firstName' , 'age'] return person.map

问题 In its most basic form, having an array of objects: let arr = [ {val:"a"}, {val:"b"} ]; How can destructuring be used, to obtain only the values ['a', 'b'] . getting the first value is easy: let [{val:res}] = arr; //res contains 'a' Obtaining all values inside the array can be done with the rest operator: let [...res] = arr; //res contains all objects Combining those, I expected to be able to use: let [...{val:res}] = arr; //undefined, expected all 'val's (['a', 'b']) The above returns

问题 These three expressions seem to be equivalent: a,b,c = line.split() (a,b,c) = line.split() [a,b,c] = line.split() Do they compile to the same code? Which one is more pythonic? 回答1: According to dis , they all get compiled to the same bytecode: >>> def f1(line): ... a,b,c = line.split() ... >>> def f2(line): ... (a,b,c) = line.split() ... >>> def f3(line): ... [a,b,c] = line.split() ... >>> import dis >>> dis.dis(f1) 2 0 LOAD_FAST 0 (line) 3 LOAD_ATTR 0 (split) 6 CALL_FUNCTION 0 9 UNPACK

问题 This question already has answers here : One-liner to take some properties from object in ES 6 (11 answers) Closed last year . Is it possible to unpack some of the keys of an object to a new object? Let's say, I want to copy 3 of the keys ( a , b , c ) from test object to a new object ( abc ). Below mention code will work. const test = {a:1, b:2, c:3, d:4, e:5 }; const {a, b, c} = test; const abc = { a, b, c, f: 6}; Is there any approach with which I can do it in a single statement? There is

问题 Is it possible to destructure an object while returning it at the same time. For example, to change this code: const mapStateToProps = ({ newItem }) =>{ const { id, name, price } = newItem; return { id, name, price }; } To something like this: const mapStateToProps = ({ newItem }) =>{ return { id, name, price } = newItem; } 回答1: No, it's not possible. (Disclaimer: your syntax works and does both destructuring and returning, but it is equivalent to ({ id, name, price } = newItem); // assigns

问题 This question already has an answer here : object destructuring: how to use intermediate nested property (1 answer) Closed 5 months ago . I have a simple use-case, but I think it's not possible with ES6 syntax. I'd like to use object destructuring to retrieve certain known properties from a nested object, but I'd also like a reference to that nested object so that I can pass it along to other functions which may care about other properties. Here's an example object: var record = { name: "foo"

问题 In the below function, I get the textarea object with the property current . Here, nested destructuring works with Start and End variables. But current variable doesn't work. function someFunction({ current: { selectionStart: Start, selectionEnd: End } }, AppStateSetter) { // do something with current, Start, and End } 回答1: The first destructuring creates only Start and End variables. If you want to create current as a variable, then you need to declare it again. function ({ current: {

问题 Hi I was going through examples of object destructuring use in passing function parameters here Object Destructuring Demo function drawES6Chart({size = 'big', cords = { x: 0, y: 0 }, radius = 25} = **{}**) { console.log(size, cords, radius); // do some chart drawing } // In Firefox, default values for destructuring assignments are not yet implemented (as described below). // The workaround is to write the parameters in the following way: // ({size: size = 'big', cords: cords = { x: 0, y: 0 },

问题 Does anyone know if you can use object destructuring with spaces in the property name? Maybe this cannot be done and I realize the JavaScript notation is incorrect but I cannot change the server json response. var obj1 = {name: 'Mr Smith', age: 21}; //destructure var {name, age} = obj1; //name='Mr Smith' and age=21 This works as expected. But when I have the following object structure can I use object destructuring or not? var obj2 = {"my name": "Mr Jones", age: 22}; var {'my name', age} =