如何将计数器变量限制在正整数范围内？

Question

我想知道如何限制计数器进入负整数范围。

var i=0;
const plus = function(){
    i += 1;
    document.querySelector("#demo").innerHTML = `Total Items : ${i}`;
}
const minus = function(){
    i -= 1;
    document.querySelector("#demo").innerHTML = `Total Items : ${i}`;
}
const clearCart = (() => {
    i = 0;
    document.querySelector("#demo").innerHTML = `Total Items : ${i}`;
})

Answer 1

您可以检查结果是否为负值并将负值替换为 0。此逻辑可以使用 Math.max:

来实现

var i=0;
const plus = function(){
    i += 1;
    document.querySelector("#demo").innerHTML = `Total Items : ${i}`;
}
const minus = function(){
    i = Math.max(i - 1, 0);
    document.querySelector("#demo").innerHTML = `Total Items : ${i}`;
}
const clearCart = (() => {
    i = 0;
    document.querySelector("#demo").innerHTML = `Total Items : ${i}`;
})

setTimeout(() => {
  plus();
  console.log('plus()');
}, 500);
setTimeout(() => {
  minus();
  console.log('minus()');
}, 1000);
setTimeout(() => {
  minus();
  console.log('minus()');
}, 1500);
setTimeout(() => {
  minus();
  console.log('minus()');
}, 2000);
setTimeout(() => {
  plus();
  console.log('plus()');
}, 2500);

<span id="demo"></span>

如何将计数器变量限制在正整数范围内？

How can a counter variable be restricted to only positive integer range?

javascript

html

css

counter