How to check the existence of a key in JavaScript Object const myObj = { a: 1, b: 2}; We need to check whether I’d exist in object or not! const result = myObj.hasOwnProperty('id'); // false Or const result = 'id' in myObj; // false Or const result = myObj.id !== undefined; // false
How to Remove Array Duplicates in ES6 Below is the sample array we have, class7 comes two times. var arr = ["class5","class7","class2","class7"]; we want to remove the duplicates value var result = [...new Set(arr)]; // result = ["class5","classs7","class2"] Now lets assume we have array object and we need to remove objects which has duplicate id var arr = [ {id: 1, name: "test"}, {id: 2, name: "test2"}, {id: 1, name: "test3"}, {id: 3, name: "test4"} ] var result = [...new Set(arr.map(({id}) => id))].map((val) => arr.find(({id}) => id === val));
We can use spread operator to add two array const result = [...arr1, ...arr2]; We can copy/clone one array/object to other variable const arr3 = [...arr1]; const obj1 = {...obj1}; Extend array value const arr4 = [ 1, 3 , ...arr1]; function myFunction(...theArgs) { // } in react we can pass all props using sprad property &lgt
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