I'd like to create an array like this by code.
let arr = {
'First': {
'bg': 'a',
'fg': 'b'
},
'Second': {
'bg': 'c',
'fg': 'd'
}
};
This doesn't work:
Uncaught TypeError: Cannot set properties of undefined (setting 'bg')
var arr = [];
arr['First']['bg'] = 'a';
arr['First']['fg'] = 'b';
arr['Second']['bg'] = 'c';
arr['Second']['fg'] = 'd';
You have to create intermediate objects before you can create the nested properties.
var arr = {};
arr['First'] = {};
arr['First']['bg'] = 'a';
arr['First']['fg'] = 'b';
arr['Second'] = {};
arr['Second']['bg'] = 'c';
arr['Second']['fg'] = 'd';
And note that you should be using {}, not []. {} is an object, [] is an array.
This will do the job:
var arr = {};
// Create the "First"
arr['First'] = {};
arr['First']['bg'] = 'a';
arr['First']['fg'] = 'b';
// Create the "Second"
arr['Second'] = {};
arr['Second']['bg'] = 'c';
arr['Second']['fg'] = 'd';
console.log(arr);