javascript - "this" inside object

Question

This question already has answers here:

Answer 1

// Your code
var wF = {
       w : 560,
       h : (312 - 42) / (560 / this.w) + 42
};

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this isn't what you think it is

Javascript has no block scope, only function scope: this inside the definition for wF does not refer to wF.

(And so this.w, whatever this is, is likely undefined. Dividing by undefined yields NaN.)

So then you might try:

// Let's not use `this`
var wF = {
       w : 560,
       h : (312 - 42) / (560 / wF.w) + 42
};

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You haven't finished defining the object yet

However, you're still defining the object where you attempt to use wF.w: it's not ready for that yet.

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Solution

So, yes, you will have to use two variables... or set up the object in stages:

// We can't even use `wF`; split up the property definitions
var wF = {};
wF.w = 560;
wF.h = (312 - 42) / (560 / wF.w) + 42;