JS的一些小练习

要求将str中的before字符串用after替换，after的首字母大小写要和before的一样：

function myReplace(str, before, after) {
  let arr=str.split(' ');
  let regex=/^[A-Z]/;
    if(arr.indexOf(before)){
      if(regex.test(before)){
        after=after[0].toUpperCase()+after.slice(1);
      }
      else{
        after=after[0].toLowerCase()+after.slice(1);
      }
      arr[arr.indexOf(before)]=after;
    }
  return arr.join(' ');
}

console.log(myReplace("A quick brown fox Jumped over the lazy dog", "Jumped", "leaped"));//A quick brown fox Leaped over the lazy dog

要求返回DNA碱基对：

/*法一：function pairElement(str) {
  let arr=str.split('');
  console.log(arr);
  for(let i=0;i<arr.length;i++){
    if(arr[i]==='G'){
      arr[i]=[arr[i],'C'];
    }
    if(arr[i]==='C'){
      arr[i]=[arr[i],"G"];
    }
    if(arr[i]==='A'){
      arr[i]=[arr[i],'T'];
    }
    if(arr[i]==='T'){
      arr[i]=[arr[i],"A"];
    }
  }
  return arr;
}*/
/*法二：function pairElement(str) {
  let matchWithBasePair = function(char, pairedArray) {
    switch (char) {
      case "A":
        pairedArray.push(["A", "T"]);
        break;
      case "T":
        pairedArray.push(["T", "A"]);
        break;
      case "C":
        pairedArray.push(["C", "G"]);
        break;
      case "G":
        pairedArray.push(["G", "C"]);
        break;
    }
  };
  const paired = [];
  for (let i = 0; i < str.length; i++) {
    matchWithBasePair(str[i], paired);
  }

  return paired;
}
 */
//法三：
function pairElement(str) {
  var pairs = {
    A: "T",
    T: "A",
    C: "G",
    G: "C"
  };
  var arr = str.split("");
  return arr.map(x => [x, pairs[x]]);
}
//调用：
console.log(pairElement("GCG"));//[ [ 'G', 'C' ], [ 'C', 'G' ], [ 'G', 'C' ] ]
console.log(pairElement("ATCGA"));//[["A","T"],["T","A"],["C","G"],["G","C"],["A","T"]]

。。。