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HTML

              
                
              
            
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CSS

              
                
              
            
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JS

              
                const arr = [1,2,3];
//1-----------------------
//map - return array
function double (x) {
  return x*2;
}
const newArr1 = arr.map(double);
console.log(newArr1);

//2-----------------------
//filter - return array
const newArr2 = arr.filter(greaterThan2);
console.log(newArr2);
function greaterThan2(x){
  return x>2;
}
//3-----------------------
//reduce - return value
function plus(x, y) {
  return x+y;
}              

//注意:reduce把数组成员从左到右,传入另一个函数,接下来把得到结果和下一个成员再一起传入那个函数
//[x1, x2, x3, x4].reduce(f) = f(f(f(x1, x2), x3), x4)
//例如:f(f(1,2),3) = f(3,3) = 6
const newArr3 = arr.reduce(plus);
console.log(newArr3);



              
            
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