You can use object spread to have an optional property: let flag1 = true; let flag2 = false; // extra cases added by Abdull let optionalKey8 = 8; let optionalKey9 = undefined; let optionalKey10 = false; let optionalKey11 = null; let optionalKey12 = “twelve”; const obj = { requiredKey1: 1, requiredKey2: 2, …(flag1 && { … Read more
I think you’re looking for the with statement, it does exactly what you are asking for: const vegetableColors = {corn: ‘yellow’, peas: ‘green’}; with (vegetableColors) { console.log(corn);// yellow console.log(peas);// green } However, it is deprecated (in strict mode, which includes ES6 modules), for good reason. destructure all properties into the current scope You cannot in … Read more
Because it’s not supported in IE, it is not supported also in Opera (see the compatibility table), but you can use the suggested polyfill: Polyfill This method has been added to the ECMAScript 2015 specification and may not be available in all JavaScript implementations yet. However, you can easily polyfill this method: if (!String.prototype.includes) { … Read more
Browser vendors don’t implement specific versions, but specific features. Almost every modern browser is still missing features from ES2017-ES2020. Hence there is not and won’t be a table where you can see an ES version to browser version mapping. But that is not a problem because you as a developer do the same. You use … Read more
Executing it in the browser console says SyntaxError: Unexpected token **. Because that’s the spec. Designed that way to avoid confusion about whether it’s the square of the negation of one (i.e. (-1) ** 2), or the negation of the square of one (i.e. -(1 ** 2)). This design was the result of extensive discussion … Read more
Two things: first, Array.find() returns the first matching element, undefined if it finds nothing. Array.filter returns a new array containing all matching elements, [] if it matches nothing. Second thing, if you want to match 4,5, you have to look into the string instead of making a strict comparison. To make that happen we use … Read more
Just check for varName === undefined. In older browsers it was possible to assign an alternate value to the global undefined variable causing that test to fail, but in ES2015+ that’s now impossible. Note that there’s no way to distinguish explicitly passing undefined as a parameter from leaving the parameter out altogether other than by … Read more
Update: The create-react-app polyfill approach and docs have changed since this question/answer. You should now include react-app-polyfill (here) if you want to support older browsers like ie11. However, this only includes the “…minimum requirements and commonly used language features“, so you’ll still want to use one of the approaches below for less common ES6/7 features … Read more
Your syntax is valid. JSX is syntax sugar for React.createElement(type) so as long as type is a valid React type, it can be used in JSX “tags”. If Button is null, your import is not correct. Maybe Button is a default export from component-library. Try: import {default as StyledButton} from “component-library”; The other possibility is … Read more
99**99 is evaluated at compile time (“constant folding”), and the compiler’s pow routine is different from the runtime one. When evaluating ** at run time, results are identical with Math.pow — no wonder since ** is actually compiled to a Math.pow call: console.log(99**99); // 3.697296376497268e+197 a = 99, b = 99; console.log(a**b); // 3.697296376497263e+197 console.log(Math.pow(99, … Read more