dojo array.push替换了上一项

Question

the following javascript returns personNames as

[{"name":"smith"},{"name":"smith"},{"name":"smith"}]

instead of

[{"name":"john"},{"name":"doug"},{"name":"smith"}]

 var personNames = []; var personName = {}; var persons = [{"firstname": "john", "id": "111"}, {"firstname": "doug", "id": "777"}, {"firstname": "smith", "id": "888"}]; if(persons.length > 0){ array.forEach(persons, function(person){ personName.name = person.firstname; personNames.push(personName); }); } 

Answer 1

First as a way to grab names you can use Array.prototype.map :

 var persons = [{"firstname": "john", "id": "111"}, {"firstname": "doug", "id": "777"}, {"firstname": "smith", "id": "888"}]; var personNames = persons.map(p => ({ name: p.firstname })); console.log(personNames); 

Then the problem with your code is that you created an object and every time you change the value of that and then push the same object to array again.

I think you forget some thing about objects and referencing. BTW this would be the correct implementation of yours:

 var persons = [{"firstname": "john", "id": "111"}, {"firstname": "doug", "id": "777"}, {"firstname": "smith", "id": "888"}]; var personNames = []; persons.forEach(p => personNames.push({ name: p.firstname })); console.log(personNames); 

Another thing to mention is that there is no need to check if there is any items in persons.

Answer 2

  array.forEach(persons, function(person){
  personName.name = person.firstname;
  personNames.push(personName);
  });

personName refers to the same object in each iteration. JavaScript keeps a reference to that object in memory, so when you update it later on, it updates everywhere, including inside the array.

For your use-case, you need to re-initialize personName each time:

  array.forEach(persons, function(person){
  personName = {};
  personName.name = person.firstname;
  personNames.push(personName);
  });

(Is the first line supposed to be persons.forEach(function(person){ ?)

Answer 3

Just use personName localy like that :

var personNames = [];

var persons = [{"firstname": "john", "id": "111"}, {"firstname": "doug", "id": "777"}, {"firstname": "smith", "id": "888"}];

if(persons.length > 0) {
    persons.forEach(element => {
      var personName = {};
      personName.name = element.firstname;
      personNames.push(personName);
    });
}
console.log(personNames); // [ { name: 'john' }, { name: 'doug' }, { name: 'smith' } ]

Answer 4

• $array.forEach() is not a function because array is not defined. Use name of the array instead ie persons.forEach() .
• Use personName locally else you will be accessing the global instance of the variable which will return the last updated value. Check code snippet at JS Bin

 var personNames = []; var persons = [{"firstname": "john", "id": "111"}, {"firstname": "doug", "id": "777"}, {"firstname": "smith", "id": "888"}]; if(persons.length > 0){ persons.forEach(function(person){ //use personName locally var personName = {}; personName.name = person.firstname; personNames.push(personName); }); } console.log(personNames); 

Answer 5

Try that

var personNames = []; 

var persons = [{"firstname": "john", "id": "111"}, {"firstname": "doug", "id": "777"}, {"firstname": "smith", "id": "888"}];
for (i = 0; i < persons.length; i++) {
   personNames.push({name:persons[i].firstname});
}