More About JS

Usefult info

• Convert string to array

    const arr = str.split('');
  
  

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• Reverse array

    arr.reverse();  // arr contains items in the reversed order
  
  

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• Convert array to string

    newStr = arr.join('');
    
  

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• array.every() Returns true / false

    array.every(val => val > 5)
  
  

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• Only consider charactersin the string, not spaces or punctuation

    // str.replace(/[^\w]/g, "")
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    let str = 'HI, THERE!!!';
  
    str = str.replace(/[^\w]/g, "").toLowerCase();
  
    console.log(str);  // output: hithere
  
  

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• Create char map object

    function createCharMap(str) {
      const charMap = {};
    
      for(let ch of str) {
        if (charMap[ch]) {
          charMap[ch]++;
        } else {
          charMap[ch] = 1;
        }
      }
    
      // charMap[char] = charMap[char] + 1 || 1;    is a shorter way
      return charMap;
    }
    
    console.log(createCharMap('hello')); // output is { h: 1, e: 1, l: 2, o: 1 }
  
  

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• Go over char map object

    for (let ch in charMap) {
      if (charMap[ch] > max) {
        max = charMap[ch];
        maxCh = ch;
      }
    }
  
  

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• Number of keys in object

    const obj = {
      a: 1,
      b: 1,
      c: 1
    }
    
    // Object.keys(obj) // returns an array of keys
    const len = Object.keys(obj).length; // 3
  
  

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• From array of objects to string

    const array = [{"name":"French"},{"name":"Lingala"},{"name":"Kongo"},{"name":"Swahili"}]
  
    console.log(array.map(Object.values).join(',')); // ---> French, Lingala, Swahili
  

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