从命令式到声明式字符限制

Question

One module in my app pulls records from a mongodb and prints out the fields for the user to see. The fields are displayed in a particular order. The order is stored in an array. The mongodb document ( pers ) may not have all of the fields possible filled out. Anyway, here is an example of my original code. It works. I want to move onto something better. I will explain as I go.

const keys = ['banana', 'orange', 'apple', 'grape']

const pers = {
    banana: 'word',
    orange: 'e t',
    apple: 'scrabble',
}
let entries = []
let entry = ''

keys.forEach(key => {
    if (pers[key]) entries.push(pers[key])
})

for (let i=0; i<entries.length; i++) {
    if ((entries.length + entries[i].length < 10) entry += '\n' + entries[i]
    else {
        console.log(entry) //message.send in my app
        entry = entries[i]
    }
}
console.log(entry)

So in my app, the message that is sent cannot be longer than 2000 characters. I am using 10 characters for the example here in the post. And I do not want them split up in the middle either. So for instance 'word' + 'et' is the maximum I can concatenate together. If I try to add 'scrabble' to it, the total length will be over 10 characters in length. So I want to send 'word et' to the console and then start the variable entry over. I also do not want to send 'word' and then 'e' and then 't' and then 'scrabble'. Like I said before, my existing code works. I just want to try and be clear on my intent.

Moving forward... Below is my second iteration of the code. I'm trying to move away from imperative statements to declarative. So I replaced the forEach block. This also works great.

const keys = ['banana', 'orange', 'apple', 'grape']

const pers = {
    banana: 'word',
    orange: 'e t',
    apple: 'scrabble',
}
let entry = ''

const entries = keys.filter(key => pers.hasOwnProperty(key)).map(key => pers[key])

for (let i=0; i<entries.length; i++) {
    if ((entries.length + entries[i].length < 10) entry += '\n' + entries[i]
    else {
        console.log(entry)
        entry = entries[i]
    }
}
console.log(entry)

The console output for both of these is:

word
e t
scrabble

That is exactly what I wanted. Now I really want to move away from that for block if possible. Surely there is a way to add another chain to my declarative statement to take care of that portion? I could possibly see a way of doing it if I didn't have the character limitation.

Anyway, if I have been unclear in any of my description or intent, please let me know and I will do my best to clarify.

Thanks!!

Answer 1

Try using .reduce like this. Your original code had a syntax error, so I'm assuming that was just a typo and not something important.

While that's functionally identical to your current code, it's still pretty convoluted. If I were you, I'd create an array of entryStrs while iterating, and then console.log them all later, like this:

 const keys = ['banana', 'orange', 'apple', 'grape'] const pers = { banana: 'word', orange: 'e t', apple: 'scrabble', } const { currentMessage, messages } = keys .filter(key => pers.hasOwnProperty(key)) .map(key => pers[key]) .reduce(({ currentMessage = '', messages = [] }, entry, i, entries) => { if (entries.length + entry.length < 10) { currentMessage += currentMessage ? ('\\n' + entry) : entry; } else { messages.push(currentMessage) currentMessage = entry; } return { currentMessage, messages }; }, {}); const allMessages = [...messages, currentMessage]; console.log(allMessages.join('\\n-----\\n-----\\n')); 

Answer 2

since in the for block you have to iterate and change an external variable and not changing anything in the array itself, you can use Conditional (tenary) Operator and replace for with forEach()

 const keys = ['banana', 'orange', 'apple', 'grape'] const pers = { banana: 'word', orange: 'e t', apple: 'scrabble', } let entry = '' const entries = keys.filter(key => pers.hasOwnProperty(key)).map(key => pers[key]) entries.forEach(e => { entries.length + e.length < 10 ? entry += '\\n' + e : (console.log(entry), entry = e) }); console.log(entry)