Every label Marta prints starts the same way. She pastes an order from the shop platform into shipping_label.py, and the script reads it as a dict. Order 1042, two dotted A5 notebooks and a lined A6 for Iris Okafor in Leeds, is today’s first. Before the JavaScript port can pick an address or a postage rate, it needs that order in a form it can read.
In this lesson, you’ll write order 1042 as a JavaScript object, read its fields, and start a label by adding and removing keys. Reading a value by its key in square brackets works as in Python, and you’ll see why JavaScript also gives you a dot for it. Begin with the order itself.
Write the Order as an Object Literal
In the Python script, the order is a dict, with every key a quoted string and None where Iris left the shipping address empty because it’s the same as her billing address:
order = {
"id": 1042,
"billing_address": {
"name": "Iris Okafor",
"street": "12 Marsh Lane",
"city": "Leeds",
"postcode": "LS6 2QA",
"country": "GB",
},
"shipping_address": None,
"insured_value": 0,
"line_items": [
{"sku": "A5-DOT", "qty": 2},
{"sku": "A6-LINED", "qty": 1},
],
"tags": ["gift", "fragile", "gift"],
"total": 46.0,
}
If you paste that into a JavaScript file, put const in front, and change None to null, it runs. Quoted keys are allowed in a JavaScript object literal, the curly-brace syntax for an object, which is JavaScript’s everyday key-value type. Each key-value pair in an object is called a property. JavaScript developers leave the quotes off the keys, though, as in this port:
const order = {
id: 1042,
billing_address: {
name: "Iris Okafor",
street: "12 Marsh Lane",
city: "Leeds",
postcode: "LS6 2QA",
country: "GB",
},
shipping_address: null,
insured_value: 0,
line_items: [
{ sku: "A5-DOT", qty: 2 },
{ sku: "A6-LINED", qty: 1 },
],
tags: ["gift", "fragile", "gift"],
total: 46.0,
};
Python needs the quotes because a bare word inside a dict literal is a variable, so {id: 1042} runs without an error and keys the dict by the built-in id() function. JavaScript reads a bare key in an object literal as the key’s own name, so id: 1042 makes a key called "id". Quotes are necessary only when a key isn’t a valid identifier, a name made of letters, digits, _, and $ that doesn’t start with a digit.
