JavaScript删除数组中的匹配项

Question

i want delete all matches in array, i have a function where i send a value, and through all matches in the array, and i delete if exist, but the array change for each splice , please look this is a litle example

var cars = ["Saab","Saab","Saab", "Volvo", "BMW","Volvo","Volvo", "BMW", "BMW", "BMW","Volvo"];

         for(j =0;j<cars.length;j++){                
                if(cars[j]=="Volvo"){
                  cars.splice(j, 1);
                }
         }
console.log(cars);

the result

["Saab", "Saab", "Saab", "BMW", "Volvo", "BMW", "BMW", "BMW"]

Answer 1

Because indexes can get messed up when looping from beginning to end of an array and removing elements, usually it's best to go backwards :

var i = cars.length - 1;

while(i >= 0) {
  if(/* condition */) {
    cars.splice(i, 1);
  }

  i--;
}

I hate native loops though (no good reason, just a personal preference), so I prefer to use semantic forEach/reduce/map/filter .

filter is actually the most semantic here (next, maybe reduce ):

var filteredCars = cars.filter(notVolvo);

function notVolvo(car) {
  return car !== 'Volvo';
}

If, for kicks and giggles, you wanted to use reduce , you could do:

var reducedCars = cars.reduce(notVolvo, []);

function notVolvo(aggregate, car) {
  return car === 'Volvo' ? aggregate : aggregate.concat([car]);
}

Answer 2

The problem is that, when you use splice to remove an item, following items will be moved one position backwards so that there is no gap.

However, your loop increases the index variable independently on whether an item was removed or not. That means that, when you delete an item, the next one will be skipped.

This can be fixed by counteracting the increment with a decrement:

for (var i=0; i<cars.length; i++)
  if (cars[i] == "Volvo")
    cars.splice(i--, 1);