应该使用什么语法来比较 else if 语句中的多个条件？

Question

I am trying to run my code to have a result of "Child" in my console. With the variable patient being 7, I still get the result of "Teenager". Any suggestions?

var patient = 7;
if (patient >= 18) {
  ageGroup = 'Adult';
} else if (patient <= 17) {
  ageGroup = 'Teenager';
} else if (patient <= 12) {
  ageGroup = 'Child';
}
console.log(ageGroup);

Answer 1

The conditions are tested in order. Since both patient <= 17 and patient <= 12 are true, the first one takes precedence, so it says they're a teenager.

When you have overlapping conditions, you can change the order so the more specific one is first. You can also use else instead of testing the last condition.

if (patient >= 18) {
  ageGroup = 'Adult';
} else if (patient <= 12) {
  ageGroup = 'Child';
} else {
  ageGroup = 'Teenager';
}

Another options is to change the conditions so they don't overlap:

if (patient >= 18) {
  ageGroup = 'Adult';
} else if (patient >= 13) {
  ageGroup = 'Teenager';
} else {
  ageGroup = 'Child';
}

Answer 2

Rather than using mnultiple if / else conditions - consider a switch statement - that is literally what it is intended for - to take conditions - compare them and allow code choices.

I also converted the single js codeblock into a function so that you coudl call it from different areas and with different ages.

Note that I am doing the comparison inside the switch statements and then returning true for the matching condition.with the default being that the passed in number is that of an adult.Also the new "let" is better than var since it is now scoped to the function it is in and not cluttering up the global scope.

 function checkAge(n) { let ageGroup; switch(true) { case n <= 12: ageGroup = 'Child'; break; case n <= 17: ageGroup = 'Teenager'; break; default: ageGroup = 'Adult' } return ageGroup; } console.log(checkAge(7)); // gives Child console.log(checkAge(15)); // gives Teenager console.log(checkAge(29)); // gives Adult

Answer 3

The programming flow defined in your IF-ELSE contains failed in logic structure: The variable with value 7 satisfy the both conditions defined in else if . Then, based in program flow, the console outputs "Teenager" because its the first condition deflected. The code bellow contains an example to resolves this problem:

var patient = 7;
if (patient >= 18) {
  ageGroup = 'Adult';
} else if (patient > 12 && patient <= 17) {
  ageGroup = 'Teenager';
} else if (patient <= 12) {
  ageGroup = 'Child';
}
console.log(ageGroup);

Answer 4

thats because of your conditions have interposition so you have two ways:

you can resolve this interposition(i suggest this way):

if (patient >= 18) {
  ageGroup = 'Adult';
} else if (patient <= 17 & patient >12) {
  ageGroup = 'Teenager';
} else if (patient <= 12) {
  ageGroup = 'Child';
}

or

you can change if statment places(i suggest this way if you have to have this interposition):

if (patient >= 18) {
  ageGroup = 'Adult';
} else if (patient <= 12) {
  ageGroup = 'Child';

} else if (patient <= 17) {
  ageGroup = 'Teenager';
}