JS: How to convert list item to lowercase and use it to get key from an object?

I have a list and an object and I would like to use a list value to get one of the keys' values.

let devices = ['001A2208B97D','001A2208C9FA','001A2214ADC8','001A2214A73A','001A2214B86E','001A2214A6DF','001A2214ADBF','001A2208CFD3']
let entities = ['Temperature', 'Valve', 'Battery', 'Offset']
let temperature = { device_class: 'temperature', icon: "hass:thermometer-bluetooth", unit: "°C"}
let valve = { device_class: '', icon: "hass:valve", unit: "%"}
let battery = { device_class: 'battery', icon: "hass:battery-bluetooth", unit: ""}
let offset = { device_class: '', icon: "hass:offset", unit: "°C" }

for (let i = 0; i < devices.length; i++) {
    for (let j = 0; j < entities.length; j++) {
        msg.payload = {
            "icon": temperature['icon'],
            "unit_of_measurement": temperature['unit'],
            "state_class": "measurement",
        }
    }
}

As you can see, the entities is lower case, so before getting the value from temperature, I need to convert to lower case.

I tried entities[0].toLowerCase()['unit'] and entities[0.toLowerCase()]['unit'] and (entities[0].toLowerCase())['unit'] and I have run out of ideas.

Does anybody know how to do this correctly? Ideally in a one liner, i.e. without first creating a new list or dict with all the lower case value. On the fly if possible :)

Solution

If this code exists in the global scope, the variable "temperature" will exist as a property of the "window" object, so you could request it like this:

window.temperature

Or this:

window["temperature"]

Or this:

var entity = "Temperature"
window[entity.toLowerCase()]

So your code might look like this:

let entities = ['Temperature', 'Valve', 'Battery', 'Offset']
let temperature = { icon: "mdi:thermometer-bluetooth", unit: "°C" }

msg.topic = window[entities[0].toLowerCase()]['unit']

But if this code is not in the global scope, such as in a function, it would work if you put the "temperature" variable inside another object, like this:

let entities = ['Temperature', 'Valve', 'Battery', 'Offset']
let stuff = {
  temperature: { icon: "mdi:thermometer-bluetooth", unit: "°C" }
}

msg.topic = stuff[entities[0].toLowerCase()]['unit']

(disclaimer: this code is completely untested)