freeCodeCamp/guide/english/certifications/javascript-algorithms-and-data-structures/intermediate-algorithm-scripting/convert-html-entities/index.md

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Convert HTML Entities

Convert HTML Entities

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Problem Explanation

• You have to create a program that will convert HTML entities from string to their corresponding HTML entities. There are only a few so you can use different methods.

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Hints

Hint 1

• You can use regular Expressions however I didn't in this case.

Hint 2

• You will benefit from a chart with all the html entities so you know which ones are the right ones to put.

Hint 3

• You should separate the string and work with each character to convert the right ones and then join everything back up.

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Solutions

Solution 1 (Click to Show/Hide)

function convertHTML(str) {
  // Split by character to avoid problems.

  var temp = str.split("");

  // Since we are only checking for a few HTML elements, use a switch

  for (var i = 0; i < temp.length; i++) {
    switch (temp[i]) {
      case "<":
        temp[i] = "&lt;";
        break;
      case "&":
        temp[i] = "&amp;";
        break;
      case ">":
        temp[i] = "&gt;";
        break;
      case '"':
        temp[i] = "&quot;";
        break;
      case "'":
        temp[i] = "&apos;";
        break;
    }
  }

  temp = temp.join("");
  return temp;
}

//test here
convertHTML("Dolce & Gabbana");

Code Explanation

• Assign temp to str.split(''), which creates an array containing each individual character in the passed in string.
• Pass each character in the newly created array into a switch() statement.
• Replace the HTML entities with their corresponding HTML entity string (i.e. '&' becomes '&' in line 51)
• temp.join('') converts the array of characters into a string to be returned.

Relevant Links

• str.split()
• arr.join()
• switch statement

Solution 2 (Click to Show/Hide)

function convertHTML(str) {
  // Use Object Lookup to declare as many HTML entities as needed.
  const htmlEntities = {
    "&": "&",
    "<": "&lt;",
    ">": "&gt;",
    '"': "&quot;",
    "'": "&apos;"
  };
  // Using a regex, replace characters with it's corresponding html entity
  return str.replace(/([&<>\"'])/g, match => htmlEntities[match]);
}

// test here
convertHTML("Dolce & Gabbana");

Code Explanation

• Create an object to use the Lookup functionality and easily find the characters.
• Use replace() to replace characters with regex.
• The first argument for replace() is a regex that catches all the target characters and puts them into a capturing group.
• The second arguments for replace() is a function with the matched character as a parameter. It returns the correspondant entity from htmlEntities.

Relevant Links

• str.replace()
• Regular Expressions

Solution 3 (Click to Show/Hide)

function convertHTML(str) {
  // Use Object Lookup to declare as many HTML entities as needed.
  const htmlEntities = {
    "&": "&",
    "<": "&lt;",
    ">": "&gt;",
    '"': "&quot;",
    "'": "&apos;"
  };
  //Use map function to return a filtered str with all entities changed automatically.
  return str
    .split("")
    .map(entity => htmlEntities[entity] || entity)
    .join("");
}

// test here
convertHTML("Dolce & Gabbana");

Code Explanation

• Create an object to use the Lookup functionality and easily find the characters.
• Split the original string by characters and use map to check for the changed html entity or use the same one.
• The a function is added which is what returns the converted entity or the original one if there is no conversion.
• Lastly we join all the characters once again.

Note that if you went the regex route then you don't need to join anything, just make sure you return the whole operation or save it to a variable and then return it.

Relevant Links

• str.split()
• arr.map()
• arr.join()