如何按元素首字母过滤 JavaScript 数组？

Question

Let say I want to search the tickers array and return all of the items in the array that start with S and then write them to the sCompanies = [].

Anyone have any idea how I go about this using a for or while loop?

// Iterate through this list of tickers to build your new array:
let tickers = ['A', 'SAS', 'SADS' 'ZUMZ'];

//console.log(tickers);



// Define your empty sCompanies array here:

//Maybe need to use const sComapnies = [] ?
let sCompanies = []


// Write your loop here:


for (i = 0; i < tickers.length; i++) {
  console.log(tickers[i]);
  
}



// Define sLength here:

sLength = 'test';

/*
// These lines will log your new array and its length to the console:
console.log(sCompanies);
console.log(sLength);*/

Answer 1

Why don't you just use the filter function like this?

// Only return companies starting by "S"
const sCompanies = tickers.filter((companyName) => companyName.startsWith('S')) 

But if you want to do it with a for loop, you can check this:

 // Iterate through this list of tickers to build your new array: const tickers = ["A", "SAS", "SADS", "ZUMZ"]; //console.log(tickers); // Define your empty sCompanies array here: const sCompanies = []; // Write your loop here: for (let i = 0; i < tickers.length; i++) { tickers[i].startsWith("S") && sCompanies.push(tickers[i]); } // Define sLength here: const sLength = sCompanies.length; /* // These lines will log your new array and its length to the console: */ console.log(sCompanies); console.log(sLength);

Answer 2

with your loop it would be like this:

for (i = 0; i < tickers.length; i++) {
  if (tickers[i].startsWith('S')) {
    sCompanies.push(tickers[i]);
  }
}

OR a bit more modern

for (const i in tickers) {
  if (tickers[i].startsWith('S')) {
    sCompanies.push(tickers[i]);
  }
}

Better yet using for...of which is for looping arrays.

for (const ticker of tickers) {
  if (ticker.startsWith('S')) {
    sCompanies.push(ticker);
  }
}

Or you could do a oneliner like the answer above.

Answer 3

This would go through the tickers array and if it starts with "S", add it to the sCompanies array.

tickers.forEach(function (item, index, array) {
    if (item.startsWith('S')) {
        sCompanies.push(item);
    }
})

Answer 4

I also got the following code back as the model solution, I understood the reason to use this format is incase I wanted to target something other than first letter:

if(tickers[i][0] == 'S')

Then I could use [1] instead of [0] to target the second letter.