【深入理解JS核心技术】14. 什么是一元函数

const unaryFunction = (a) => console.log(a + 10); // Add 10 to the given argument and display the value
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function getProduct(a, b, c = 1) { 
 return a * b * c; 
} 

let getSum = (a, b, c = 0) => { 
 return a + b + c; 
} 

console.log(getProduct(...[1,2])); // 2 
console.log(getProduct(...[1,2,3])); // 6 
console.log(getProduct(...[1,2,3,4])); // 6 

console.log(getSum(...[0,1])); // 1 
console.log(getSum(...[0,1,2])); // 3 
console.log(getSum(...[0,1,2,3])); // 3
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function getSum(...values) {
 // 顺序累加values中的所有值
 // 初始值的总和为0
 return values.reduce((x,y) => x + y, 0);
}
console.log(getSum(1,2,3)); // 6
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// 不可以
function getProduct(...values, lastValue) {} 

// 可以
function ignoreFirst(firstValue, ...values) { 
 console.log(values); 
} 

ignoreFirst(); // [] 
ignoreFirst(1); // [] 
ignoreFirst(1,2); // [2] 
ignoreFirst(1,2,3); // [2, 3]
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let getSum = (...values) => { 
 return values.reduce((x, y) => x + y, 0); 
} 

console.log(getSum(1,2,3)); // 6
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function getSum(...values) { 
 console.log(arguments.length); // 3 
 console.log(arguments); // [1, 2, 3] 
 console.log(values); // [1, 2, 3] 
} 

console.log(getSum(1,2,3));
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