One approach is using Array.prototype.entries(): for (const [i, value] of arr.entries()) { if (i === arr.length – 1) { // do your thing } } Another way is keeping a count outside the loop like Shidersz suggested. I don’t think you want to check indexOf(item) though because that poses a problem if the last item … Read more
Option 1: Interpolation We can create interpolation blocks that return an empty string, and embed the comments inside them. const fields = ` id,${ /* post id */” } message,${ /* post status/message */” } created_time, permalink_url, type `; console.log(fields); Option 2: Tagged Templates Using tagged templates we can clear the comments and reconstruct the … Read more
You can call a generator step by step using next function var sequence = fibonacci(); var value; while ((value = sequence.next()) < 1000) { console.log(value); } plus, maybe even a nicer solution would be something like: function* fibonacci(limit){ let previous = 0; let current = 1; while(previous + current < limit) { let temp = … Read more
When you create a class class Foo extends Bar { constructor(a, b) { } } you can later add methods to this class by assigning to its prototype: // methodA(a, b) in class Foo Foo.prototype.methodA = function(a, b) { // do whatever… } You can also add static methods similarly by assigning directly to the … Read more
Can’t you do person instanceof Person? Comparing constructors alone won’t work for subclasses
You should just write a class without a constructor and see if it works 🙂 From the same docs As stated, if you do not specify a constructor method a default constructor is used. For base classes the default constructor is: constructor() {} For derived classes, the default constructor is: constructor(…args) { super(…args); }
throw Object.assign( new Error(myMessage), { code: 402 } ); Throw a regular error and extend it with custom fields. You could also write a reusable error class for that: class CodeError extends Error { constructor(message, code) { super(message); this.code = code; } } throw new CodeError(myMessage, 404); That way, you can distinguish the errors easily … Read more
There is a more simpler solution you can try. const mapObject = new Map(); mapObject.set(1, ‘hello’); console.log([…mapObject.entries()]); // [[1, “hello”]] console.log([…mapObject.keys()]); // [1] console.log([…mapObject.values()]); // [“hello”]
I think the simplest way to check if the function is ES6 class is to check the result of .toString() method. According to the es2015 spec: The string representation must have the syntax of a FunctionDeclaration FunctionExpression, GeneratorDeclaration, GeneratorExpression, ClassDeclaration, ClassExpression, ArrowFunction, MethodDefinition, or GeneratorMethod depending upon the actual characteristics of the object So the … Read more