comparing two arrays before adding an item from on

问题:

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Closed 3 years ago.

I have two arrays.

var addFrom = ["orange", "banana", "watermelon", "lemon", "peach"];
var addTo = ["pear", "tangerine", "grape", "orange", "blueberry"];

I would like to check if the first item in "addFrom" array is already in "addTo" array.

If the "addTo" array does not have the first item in "addFrom" array, I would like to push this item to "addTo" array.

However, if the first item in the "addFrom" array is already in the "addTo" array, I would like to move on to the second item in the "addFrom" array and do the same thing until I find the item in the "addFrom" array that is not in the "addTo" array, which will then be pushed to the "addTo" array. and I want to add only one item to the "addTo" array.

As a result, I want the "addTo" array to look like this:

var addTo = ["pear", "tangerine", "grape", "orange", "blueberry", "banana"];

How can I do this in JavaScript?

回答1:

You could use Array#some() and stop the iteration if one item is not in the addTo array.

var addFrom = ["orange", "banana", "watermelon", "lemon", "peach"],
    addTo = ["pear", "tangerine", "grape", "orange", "blueberry"];

addFrom.some(function (a) {
    if (!~addTo.indexOf(a)) {
        addTo.push(a);
        return true;
    }
});

document.write('<pre> ' + JSON.stringify(addTo, 0, 4) + '</pre>');

回答2:

A simple loop seems the best approach here (I've used while).

var i = -1, len = addFrom.length;
while (++i < len) {
  if (addTo.indexOf(addFrom[i]) === -1) {
    addTo.push(addFrom[i]);
    break;
  }
}

DEMO

回答3:

var addFrom = ["orange", "banana", "watermelon", "lemon", "peach"];
var addTo = ["pear", "tangerine", "grape", "orange", "blueberry"];

for(var i = 0; i < addFrom.length; i++){   
    if(addTo.indexOf(addFrom[i]) === -1 ){
        addTo.push(addFrom[i]); 
        break; 
    }    
}

回答4:

https://jsfiddle.net/povvx8hg/

var addFrom = ["orange", "banana", "watermelon", "lemon", "peach"];
var addTo = ["pear", "tangerine", "grape", "orange", "blueberry"];

for (i = 0; i < addFrom.length; i++) {
    if(addTo.indexOf(addFrom[i]) != -1) {
    console.log("Exist");
  } else {
    addTo.push(addFrom[i]);
  }
}

console.log(addTo);

回答5:

Easy peasy

for (index = 0; index < addFrom.length; ++index) {
  if (addTo.indexOf(addFrom[index]) === -1){
      addTo.push(addFrom[index]);
      break;
  }
}

回答6:

You can use forEach

var addFrom = ["orange", "banana", "watermelon", "lemon", "peach"];
var addTo = ["pear", "tangerine", "grape", "orange", "blueberry"];
var inserted = false;

    addFrom.forEach(function(v,i){
        if(inserted)
           return;

        if(addTo.indexOf(v)<0)
        {
            addTo.push(v);
            inserted = true;
        }
    })