JavaScript foreach 一个数组并用逗号分隔它们，最后一个逗号用“and”

Question

I need to know how I can split an array with commas and if it's the last one element to the last one I have , and and if it's the last one I add . to it. I have the following code. The output as one big string honda, audi, tesla, and toyota. the following is printing more than one. Also what if I wanted to push it one time into new array. So one big array of string ["honda, audi, tesla, and toyota."]

 let namesArray = ["honda", "audi", "tesla", "toyota"]; let newOrder = "" namesArray.forEach((item, index) => { console.log(index); if (index === namesArray.length - 2) { newOrder = item + ', and' } else if (index === namesArray.length - 1) { newOrder = (item + '.') } else { newOrder = (item + ',') } }) console.log('new string ', newOrder)

"new string ", "honda,audi,tesla,toyota."

Answer 1

In terms of what is wrong with your existing code, you are not adding the new string value to your output (ie use newOrder += , not newOrder = in the loop):

 let namesArray = ["honda", "audi", "tesla", "toyota"]; let newOrder = "" namesArray.forEach((item, index) => { if (index === namesArray.length - 2) { newOrder += item + ', and ' } else if (index === namesArray.length - 1) { newOrder += (item + '.') } else { newOrder += (item + ', ') } }) console.log(newOrder)

It would be simpler though to just join a slice of the array from the start to the second to last element, then add , and and the last element to that string:

 let namesArray=["honda", "audi", "tesla", "toyota"]; let newOrder = namesArray.slice(0,-1).join(', ') + ', and ' + namesArray.slice(-1) + '.'; console.log(newOrder)

Answer 2

You can easily achieve this result using map and join

 const arr = ["honda", "audi", "tesla", "toyota"]; const result = arr.map((item, index) => { if (index === arr.length - 1) { return `and ${item}.`; } else { return `${item}, `; } }).join(""); console.log(result);

You can also use string template literal if the array size in known prior

 const arr = ["honda", "audi", "tesla", "toyota"]; const [a, b, c, d] = arr; const result = `${a}, ${b}, ${c}, and ${d}.`; console.log(result);

Answer 3

I would create a function for reuse. First make a .slice() of your array, so the original is not affected. .pop() off the last Array element. Then .join(', ') and concatenate +', and ' along with the element you popped off +'.' .

 function andIt(array){ const a = array.slice(), p = a.pop()+'.'; if(.a;length){ return p. } return a,join(', ')+'; and '+p, } const namesArray = ['honda', 'audi', 'tesla'; 'toyota']. console;log(andIt(namesArray)). console;log(andIt(['test']));