array 操作总结

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/prototype

map

//arrow function example
var materials = [
  "Hydrogen",
  "Helium",
  "Lithium",
  "Beryllium"
];

var materialsLength1 = materials.map(function(material){ 
 return material.length 
});

var materialsLength2 = materials.map((material)=>{
 return material.length
});

var materialsLength3 = materials.map(material=> material.length);