Exploring the Function of "RegExp.exec" in TypeScript

Question

Exploring the Function of "RegExp.exec" in TypeScript

Attempting to utilize the "exec" method in RegExp, I have written the following code:

let result = <RegExpExecArray>{};
while (result = expressionCheck.exec(text)) {
    let matchIndex = result.index;
    let t = result[0].length;
    matchRanges.push(new RegRange(matchIndex, t));
}

However, an error is being thrown stating:

Build:Type 'RegExpExecArray | null' is not assignable to type 'RegExpExecArray'.

I attempted to modify the loop condition to :

while ((result = expressionCheck.exec(text)) != null) {

Even after this adjustment, it continues to not work. How should the loop condition be written for this scenario?

typescript

Answer 1

Answer №1

To properly format the code, you should follow this structure:

let output;
while ((output = expression.exec(text)) !== null) {
    let matchPosition = output.index;
    let lengthValue = output[0].length;
    matchingRanges.push(new RegRange(matchPosition, lengthValue));
}

The reason why the original code is incorrect: The original code incorrectly stated that result was of type RegExpExecArray. However, this type does not align with the return type of exec, which is RegExpExecArray | null. Even though it attempted to narrow down the possibilities using !== null, the code could still assign null to

result</code, leading to an error.</p>

<p>An alternative way to write the code is as follows:</p>

<pre><code>for (let output = expression.exec(text); output !== null; output = expression.exec(text)) {
  const matchPosition = output.index;
  const lengthValue = output [0].length;
  matchingRanges.push(new RegRange(matchPosition, lengthValue));
}

Answer 2

To properly format the code, you should follow this structure:

let output;
while ((output = expression.exec(text)) !== null) {
    let matchPosition = output.index;
    let lengthValue = output[0].length;
    matchingRanges.push(new RegRange(matchPosition, lengthValue));
}

The reason why the original code is incorrect: The original code incorrectly stated that result was of type RegExpExecArray. However, this type does not align with the return type of exec, which is RegExpExecArray | null. Even though it attempted to narrow down the possibilities using !== null, the code could still assign null to

result</code, leading to an error.</p>

<p>An alternative way to write the code is as follows:</p>

<pre><code>for (let output = expression.exec(text); output !== null; output = expression.exec(text)) {
  const matchPosition = output.index;
  const lengthValue = output [0].length;
  matchingRanges.push(new RegRange(matchPosition, lengthValue));
}

Answer 3

Answer №2

I prefer using String.prototype.matchAll because it allows for easy destructuring:

const [[group1, group2]] = [...text.matchAll(expressionCheck)];

According to MDN, this is recommended as an alternative and you can find more information in the documentation.

Answer 4

I prefer using String.prototype.matchAll because it allows for easy destructuring:

const [[group1, group2]] = [...text.matchAll(expressionCheck)];

According to MDN, this is recommended as an alternative and you can find more information in the documentation.

Answer 5

Answer №3

I needed to extract hours and minutes from the given string below:

18h:20m

To achieve this, I crafted the following regex pattern:

const [, hours, minutes] = /^(\d+)[:h -]\s?(\d+)m?$/.exec(string) || ['', '', ''];

You have the flexibility to adjust it based on the specific number of matches you want to retrieve.

Please note that exec() will output all found matches as strings.

Answer 6

I needed to extract hours and minutes from the given string below:

18h:20m

To achieve this, I crafted the following regex pattern:

const [, hours, minutes] = /^(\d+)[:h -]\s?(\d+)m?$/.exec(string) || ['', '', ''];

You have the flexibility to adjust it based on the specific number of matches you want to retrieve.

Please note that exec() will output all found matches as strings.

Exploring the Function of "RegExp.exec" in TypeScript

Answer №1

Answer №2

Answer №3

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