- Use typeof to check if a value is classified as a symbol primitive.
//#Source https://bit.ly/2neWfJ2 const isSymbol = val => typeof val === 'symbol'; console.log(isSymbol(Symbol('x'))); console.log(isSymbol(Symbol(1))); console.log(isSymbol(Symbol(')')));
true true true
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ECMAScript 6 introduced String.prototype.includes:
const string = "foo"; const substring = "oo"; console.log(string.includes(substring));
includes doesn't have Internet Explorer support, though. In ECMAScript 5 or older environments, use String.prototype.indexOf, which returns -1 when a substring cannot be found:
var string = "foo"; var substring = "oo"; console.log(string.indexOf(substring) !== -1);
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