英文:
If I set the value to find as a variable, why doesn't it work?
问题
当使用数字1调用findProd函数时，一切都正常。但是，如果我用idToFind变量替换数字1，控制台会输出undefined。为什么会发生这种情况？
P.S. 在我的文件中，如果我打印idToFind，结果是1。需要使函数的比较值动态化。
英文:
When calling the findProd function with the number 1, everything works correctly. However, if I replace the number 1 with the idToFind variable, the console outputs undefined. Why is this happening?
P.S. in my file, if I print idToFind, the result is 1.
addToCartButtons.forEach(button => {
button.addEventListener('click', (event) => {
const idToFind = event.target.dataset.id;
let array = [{id: 1, name: 'mattia'}, {id: 2, name: 'cesare'}];
function findProd(product) {
return product.id === 1;
}
const result = array.find(findProd);
console.log(result);
})
});
I need to make the comparison value of the function dynamic.
答案1
得分: 2
因为event.target.dataset.id是一个字符串。你所使用的严格比较运算符首先比较数据类型，所以1 === '1' 的结果是false。
请注意，你可以使用一元运算符+将字符串值转换为数字值。然后1 === 1 就会得到true，因此，你的find函数将按预期工作。
addToCartButtons.forEach(button => {
button.addEventListener('click', (event) => {
const idToFind = +event.target.dataset.id;
let array = [{id: 1, name: 'mattia'}, {id: 2, name: 'cesare'}];
const result = array.find((product) => product.id === idToFind);
console.log(result);
})
});
此外，从代码的可读性角度来看，将标识符在变量初始化期间转换为数字会使代码更加清晰。
你可能想要阅读更多关于严格相等性 ===的信息。
英文:
It's because the event.target.dataset.id is a string. The strict comparison operator you use compares types first, so 1 === '1' results in false.
Notice how you can convert string value to a number value with an unary +. Then 1 === 1 would result in true and in consequence, your find function will work as expected.
addToCartButtons.forEach(button => {
button.addEventListener('click', (event) => {
const idToFind = event.target.dataset.id;
let array = [{id: 1, name: 'mattia'}, {id: 2, name: 'cesare'}];
function findProd(product) {
return product.id === +idToFind;
}
const result = array.find(findProd);
console.log(result);
})
});
Also, the code would benefit in readability from using an array function and converting the identifier to number during the variablie initialization.
addToCartButtons.forEach(button => {
button.addEventListener('click', (event) => {
const idToFind = +event.target.dataset.id;
let array = [{id: 1, name: 'mattia'}, {id: 2, name: 'cesare'}];
const result = array.find((product) => product.id === idToFind);
console.log(result);
})
});
You may want to read more about the strict equality ===.
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