Raw string access

Raw String Access in ECMAScript 6

ECMAScript 6 introduced template strings, among which raw string access is an easily overlooked yet highly practical feature. It allows developers to obtain the raw content of template strings, bypassing the processing of escape characters and directly outputting the string in its original form.

Basic Concept of Raw Strings

In JavaScript, the backslash (\) in strings is typically used as an escape character. For example, \n represents a newline, and \t represents a tab. However, in certain scenarios, we may need to access the raw form of the string, including the escape characters themselves.

ES6 provides the String.raw tag function to access the raw content of template strings:

const path = String.raw`C:\Development\profile\about.html`;
console.log(path); // Output: C:\Development\profile\about.html

Without String.raw, the backslashes would be interpreted as escape characters:

const path = `C:\Development\profile\about.html`;
console.log(path); // Output: C:Developmentprofileabout.html

How String.raw Works

String.raw is a tag function. Its first argument is an object containing a raw property, which is an array storing the raw segments of the split template string:

const tag = (strings, ...values) => {
  console.log(strings.raw[0]); // Outputs the raw string segment
  console.log(strings[0]);      // Outputs the processed string segment
};

tag`Hello\nWorld`;
// strings.raw[0] outputs: "Hello\\nWorld"
// strings[0] outputs: "Hello\nWorld"

Practical Use Cases

Escape Characters in Regular Expressions

When writing regular expressions, a large number of backslashes are often required. Using raw strings avoids double escaping:

const regex = String.raw`\d+\.\d+`;
console.log(regex); // Output: \d+\.\d+
// Equivalent to
const regex2 = new RegExp("\\d+\\.\\d+");

Handling Windows File Paths

Raw strings are particularly useful when dealing with Windows file paths:

const filePath = String.raw`C:\Users\Public\Documents\report.docx`;
console.log(filePath); // Correctly outputs the path

Preserving Multiline Strings in Their Original Form

When maintaining the original format of multiline strings:

const poem = String.raw`
  Bright moonlight before my bed,
  Perhaps frost on the ground.
  I lift my head to gaze at the moon,
  Lower it to think of home.
`;
console.log(poem);
// Outputs the original format, including line breaks and indentation

Custom Raw String Processors

We can create our own tag functions to mimic the functionality of String.raw:

function myRaw(strings, ...values) {
  let result = '';
  for (let i = 0; i < strings.length; i++) {
    result += strings.raw[i];
    if (i < values.length) {
      result += values[i];
    }
  }
  return result;
}

const str = myRaw`Hello\u{41}\nWorld`;
console.log(str); // Output: Hello\u{41}\nWorld

Comparison with Regular Strings

The table below highlights the differences between raw strings and regular strings:

// Comparison example
const normalStr = `Hello\nWorld`;
const rawStr = String.raw`Hello\nWorld`;

console.log(normalStr);  // Outputs two lines
console.log(rawStr);     // Outputs "Hello\nWorld"

Performance Considerations

Using String.raw incurs a slight performance overhead because it requires creating additional objects to store raw string information. However, in most cases, this overhead is negligible. It should only be considered in extreme performance-sensitive scenarios.

Browser Compatibility

All modern browsers support String.raw, including:

• Chrome 41+
• Firefox 34+
• Edge 12+
• Safari 9+
• Opera 28+

For older browsers, tools like Babel can be used for transpilation, or a polyfill can be implemented:

if (!String.raw) {
  String.raw = function(strings, ...values) {
    // Polyfill implementation
  };
}

Integration with Other Language Features

Raw strings can seamlessly integrate with other ES6+ features:

// Combined with destructuring assignment
const [first, second] = String.raw`one\ntwo`.split('\\n');
console.log(first, second); // Output: one two

// Combined with arrow functions
const logRaw = str => console.log(String.raw(str));
logRaw`test\nexample`; // Output: test\nexample

Common Pitfalls

1. Mistaking String.raw for a method:

   // Incorrect usage
   String.raw("test"); // TypeError
   
   // Correct usage
   String.raw`test`;
   

2. Forgetting that raw strings still process template variables:

   const name = "Alice";
   console.log(String.raw`Hello ${name}\n`); 
   // Output: Hello Alice\n
   

3. Confusing raw strings with JSON strings:

   // This is not JSON
   const notJson = String.raw`{"key": "value"}`;
   // Additional processing is needed to convert to an object