Javascript不等于和OR

Question

This looks a simple code but not sure what I am doing wrong here.

var data = "[{\"Id\":\"01\",\"Name\":\"01- Alabama\"},{\"Id\":\"02\",\"Name\":\"02- Arizona\"},{\"Id\":\"03\",\"Name\":\"03- Arkansas\"}]";

 var myJson = JSON.parse(data);
 for (var key in myJson) {
   var item = {
   Id: myJson[key].Id,
   Name: myJson[key].Name
 };

 if(item.Id != "01" || item.Id !="02")
 {
   alert(item.Id);   
 }
}

I am expecting to just show an alert as "03" but it shows 3 alert each for "01", "02" & "03"

Looks like != and OR operator not working ?

Answer 1

The || operator only returns false when both of its operands are false (and true in all other cases).

The && operator only returns true when both of its operands are true (and false in all other cases).

You have to use && instead of || in the if condition to get the expected result:

 var data = "[{\\"Id\\":\\"01\\",\\"Name\\":\\"01- Alabama\\"},{\\"Id\\":\\"02\\",\\"Name\\":\\"02- Arizona\\"},{\\"Id\\":\\"03\\",\\"Name\\":\\"03- Arkansas\\"}]"; var myJson = JSON.parse(data); for (var key in myJson) { var item = { Id: myJson[key].Id, Name: myJson[key].Name }; if(item.Id != "01" && item.Id !="02") { alert(item.Id); } } 

Answer 2

Actually is working as expected because the OR operator is returning true for cases when Id == 01 and Id == 02

What you want to do is to join the two operands with AND operator && and this way execute the logic just when Id != 01 AND Id != 02 .

 var data = "[{\\"Id\\":\\"01\\",\\"Name\\":\\"01- Alabama\\"},{\\"Id\\":\\"02\\",\\"Name\\":\\"02- Arizona\\"},{\\"Id\\":\\"03\\",\\"Name\\":\\"03- Arkansas\\"}]"; var myJson = JSON.parse(data); for (var key in myJson) { var item = { Id: myJson[key].Id, Name: myJson[key].Name }; if (item.Id != "01" && item.Id != "02") { alert(item.Id); } } 

Answer 3

item.Id != "01" || item.Id !="02" item.Id != "01" || item.Id !="02" will always be true, as it can't be equal to both of the values at the same time.

You only need to use && instead of || :

 var data = "[{\\"Id\\":\\"01\\",\\"Name\\":\\"01- Alabama\\"},{\\"Id\\":\\"02\\",\\"Name\\":\\"02- Arizona\\"},{\\"Id\\":\\"03\\",\\"Name\\":\\"03- Arkansas\\"}]"; var myJson = JSON.parse(data); for (var key in myJson) { var item = { Id: myJson[key].Id, Name: myJson[key].Name }; if(item.Id != "01" && item.Id !="02") { console.log(item.Id); // I prefer consoling, that's less agressive! } } 

⋅ ⋅ ⋅

If you also plan to do if(item.Id != "01" && item.Id !="02" && item.Id !="03") , you must want to use a > comparator and unary + on your string:

 var data = "[{\\"Id\\":\\"01\\",\\"Name\\":\\"01- Alabama\\"},{\\"Id\\":\\"02\\",\\"Name\\":\\"02- Arizona\\"},{\\"Id\\":\\"03\\",\\"Name\\":\\"03- Arkansas\\"}]"; var myJson = JSON.parse(data); for (var key in myJson) { var item = { Id: myJson[key].Id, Name: myJson[key].Name }; if(+item.Id > 2) { console.log(item.Id); // I prefer consoling, that's less agressive! } } 

Hope it helps.