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To check if a string is a valid SHA256 hash in JavaScript, we can use a regex expression to match for the 64 consecutive hexadecimal digits which are characters from a-f and numbers from 0-9.

TL;DR

// Regular expression to check if string is a SHA256 hash
const regexExp = /^[a-f0-9]{64}$/gi;

// String with SHA256 hash
const str = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad";

regexExp.test(str); // true

This is the regex expression for matching almost all the test cases for a valid SHA256 hash in JavaScript.

// Regular expression to check if string is a SHA256 hash
const regexExp = /^[a-f0-9]{64}$/gi;

This will match all the 64 hexadecimal digits which have characters in the range from a till f and numbers from 0 till 9.

Now let's write a string with SHA256 hash like this,

// Regular expression to check if string is a SHA256 hash
const regexExp = /^[a-f0-9]{64}$/gi;

// String with SHA256 hash
const str = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad";

Now to test the string, we can use the test() method available in the regular expression we defined. It can be done like this,

// Regular expression to check if string is a SHA256 hash
const regexExp = /^[a-f0-9]{64}$/gi;

// String with SHA256 hash
const str = "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad";

regexExp.test(str); // true

• The test() method will accept a string type as an argument to test for a match.
• The method will return boolean true if there is a match using the regular expression and false if not.

See the above example live in JSBin.

If you want this as a utility function which you can reuse, here it is,

/* Check if string is a valid SHA256 Hash */
function checkIfValidSHA256(str) {
  // Regular expression to check if string is a SHA256 hash
  const regexExp = /^[a-f0-9]{64}$/gi;

  return regexExp.test(str);
}

// Use the function
checkIfValidSHA256(
  "ba7816bf8f01cfea414140de5dae2223b00361a396177a9cb410ff61f20015ad"
); // true
checkIfValidSHA256("hello98123!"); // false

That's all! 😃

Feel free to share if you found this useful 😃.

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