How do I test if a variable does not equal either of two values?

问题

I want to write an if/else statement that tests if the value of a text input does NOT equal either one of two different values. Like this (excuse my pseudo-English code):

var test = $("#test").val();
if (test does not equal A or B){
    do stuff;
}
else {
    do other stuff;
}

How do I write the condition for the if statement on line 2?

回答1:

Think of ! (negation operator) as "not", || (boolean-or operator) as "or" and && (boolean-and operator) as "and". See Operators and Operator Precedence.

Thus:

if(!(a || b)) {
  // means neither a nor b
}

However, using De Morgan's Law, it could be written as:

if(!a && !b) {
  // is not a and is not b
}

a and b above can be any expression (such as test == 'B' or whatever it needs to be).

Once again, if test == 'A' and test == 'B', are the expressions, note the expansion of the 1st form:

// if(!(a || b)) 
if(!((test == 'A') || (test == 'B')))
// or more simply, removing the inner parenthesis as
// || and && have a lower precedence than comparison and negation operators
if(!(test == 'A' || test == 'B'))
// and using DeMorgan's, we can turn this into
// this is the same as substituting into if(!a && !b)
if(!(test == 'A') && !(test == 'B'))
// and this can be simplified as !(x == y) is the same as (x != y)
if(test != 'A' && test != 'B')

回答2:

ECMA2016 Shortest answer, specially good when checking againt multiple values:

if (!["A","B", ...].includes(test)) {}

回答3:

In general it would be something like this:

if(test != "A" && test != "B")

You should probably read up on JavaScript logical operators.

回答4:

I do that using jQuery

if ( 0 > $.inArray( test, [a,b] ) ) { ... }

回答5:

var test = $("#test").val();
if (test != 'A' && test != 'B'){
    do stuff;
}
else {
    do other stuff;
}

回答6:

You used the word "or" in your pseudo code, but based on your first sentence, I think you mean and. There was some confusion about this because that is not how people usually speak.

You want:

var test = $("#test").val();
if (test !== 'A' && test !== 'B'){
    do stuff;
}
else {
    do other stuff;
}

回答7:

May I suggest trying to use in else if statement in your if/else statement. And if you don't want to run any code that not under any conditions you want you can just leave the else out at the end of the statement. else if can also be used for any number of diversion paths that need things to be a certain condition for each.

if(condition 1){

} else if (condition 2) {

}else {

}

来源：https://stackoverflow.com/questions/6115801/how-do-i-test-if-a-variable-does-not-equal-either-of-two-values

标签

javascript