Syntax error in object property assignment

Question

Code Academy says there are 2 ways to create objects in JavaScript.

1. object literal notation

var myObject = {     
    key: value,     
    key: value,    
    key: value 
};

2. object constructor approach

var myObject = new Object();

Keys can then be added thus:

myObj["name"] = "Charlie"; 
myObj.name = "Charlie"; //shorthand for the first

Being asked to create 3 objects, I tried different ways to produce the objects with the same values but I am getting an error using the template provided above. My code is pasted below:

var object1 = {
    1: 2,
    7: 3,
    4: 5
};

var object2 = new Object();
object2['1'] = 2;
object2['7'] = 3;
object2['4'] = 5;

var object3 = new Object();
object3.1 = 2;
object3.7 = 3;
object3.4 = 5;

Code Academy gave me an error and to figure out where exactly it was, I used Chrome's console. Tying each object creation separately on Chrome's console, object1 and object2 could be created but not object3 which produces the error: Uncaught SyntaxError: Unexpected number

Changing object3's code to (changing keys from numbers to strings):

var object3 = new Object();
object3.'1' = 2;
object3.'7' = 3;
object3.'4' = 5;

produces the error: Uncaught SyntaxError: Unexpected string

Is it possible to create object3 using this template/layout to produce values of object1 or can the key never be a number or string? A string but not a number for the key worked in creating object2.

A property name can't start with a number using 'dot' syntax. object3._1 will work, however because underscores (as well as $ and alphabetical characters) are legal syntax. — Bob Gear
– Bob Gear, Commented Feb 16, 2017 at 22:05

ibrahim mahrir · Accepted Answer · 2017-02-16 22:13:52Z

2

When using the dot notation, the keys should be named in the same way variables are (starts with a letter or _ and contains only letters, numbers and _).

If the key is not valid to be used as dot notation then it can be used using bracket notation like this:

obj["key goes here"];

Since 1, 7 and 4 are not valid for dot notation, the only way to use them as key is like this: obj["4"] ...

Here is an MDN page about the basics of objects.

Example:

These keys are valid for dot notation:

abc;
_a;
R2D2;
_;
_0;
a________a;

Thes are not:

k-ey;
a b a;
99;
k.e.y;
@@;

edited Feb 16, 2017 at 22:13

answered Feb 16, 2017 at 22:06

ibrahim mahrir

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