You can use array.filter, this takes a function that is passed each item of the array and returns true or false and returns a new array that only has items where the function passed to filter will return true. You can partially apply a curried function. Example of curried function: const plus = a => … Read more
No, there is no way to access the object literal that is currently being defined from within the definition itself. If you want to set properties based on the values of other properties, then you either need to base them both on some external value (that is not a property itself) or run an initializer … Read more
Unless the variable k is defined, that’s probably what’s causing your trouble. Something like this will do what you want: var new_tweets = { }; new_tweets.k = { }; new_tweets.k.tweet_id = 98745521; new_tweets.k.user_id = 54875; new_tweets.k.data = { }; new_tweets.k.data.in_reply_to_screen_name=”other_user”; new_tweets.k.data.text=”tweet text”; // Will create the JSON string you’re looking for. var json = JSON.stringify(new_tweets); … Read more
You can use an utility function like this: get = function(obj, key) { return key.split(“.”).reduce(function(o, x) { return (typeof o == “undefined” || o === null) ? o : o[x]; }, obj); } Usage: get(user, ‘loc.lat’) // 50 get(user, ‘loc.foo.bar’) // undefined Or, to check only if a property exists, without getting its value: has … Read more
The second line is giving you a SyntaxError because the { token at the beginning of it causes an ambiguity, the parser treats it as if it were a Block statement, not the start of an object literal. For example, a valid Block statement: { foo: ‘bar’ } The above looks like an object literal, … Read more
In ECMAScript, starting from ES5, reserved words may be used as object property names “in the buff”. This means that they don’t need to be “clothed” in quotes when defining object literals, and they can be dereferenced (for accessing, assigning, and deleting) on objects without having to use square bracket indexing notation. That said, reserved … Read more
I have researched this a bit. MDN is silent on the issue, and so is the spec (ES5, ES6). They only state that the property accessor must be a string, without any qualifications – in other words, there is no limit as far as the spec is concerned. That’s hardly surprising. How browsers handle it, … Read more
What is an applicable example of using Maps over objects? I think you’ve given one good example already: You at least need to use Maps when you are using objects (including Function objects) as keys. in particular, “when would keys be unknown until runtime?” Whenever they are not known at compile time. In short, you … Read more
Object.keys might be a solution: Object.keys({ dbm: -45}); // [“dbm”] The differences between for-in and Object.keys is that Object.keys returns all own key names and for-in can be used to iterate over all own and inherited key names of an object. As James Brierley commented below you can assign an unknown property of an object … Read more
The really short answer to both your questions is that when you make one variable equal to another, a COPY of what’s in the first variable is made and stored in the second variable – there is no linkage between the two variables. But, read on for more details and why it can seem like … Read more