ES6字符串模板，剩余参数，默认参数功能与用法示例

//产生一个随机数
var num=Math.random();
//将这个数字输出到console
console.log(`your num is ${num}`);

containsAll("banana", "b", "nan") //会返回 true,
containsAll("banana", "c", "nan") //会返回 false。

function containsAll(haystack) {
 for (var i = 1; i < arguments.length; i++) {
  var needle = arguments[i];
  if (haystack.indexOf(needle) === -1) {
   return false;
  }
 }
 return true;
}

function containsAll(haystack, ...needles) {
 for (var needle of needles) {
  if (haystack.indexOf(needle) === -1) {
   return false;
  }
 }
 return true;
}

var a = [2,3,4];
var b = [ 1, ...a, 5 ];
console.log( b );// [1,2,3,4,5]

function animalSentence(animals2="tigers", animals3="bears") {
  return `Lions and ${animals2} and ${animals3}! Oh my!`;
}

animalSentence()//"Lions and tigers and bears! Oh my!"；
animalSentence("elephants") //"Lions and elephants and bears! Oh my!"
animalSentence("elephants", "whales")//"Lions and elephants and whales! Oh my!".

function animalSentenceFancy(animals2="tigers",animals3=(animals2 == "bears") ? "sealions" : "bears")
{
 return `Lions and ${animals2} and ${animals3}! Oh my!`;
}