Tips on halting or advancing through nested for each loops in TypeScript

When attempting to use the break statement inside a nested forEach loop in TypeScript, an error message stating "jump target cannot cross function boundary" is displayed. I am looking for a solution on how to break out of a nested forEach loop when a certain condition is met.


groups = [object-A, object-B, object-C]
groups.forEach(function (group) {
    // names also an array
    group.names.forEach(function (name) {

        if (name == 'SAM') {
            break; //cannot use break here as it says jump target cannot cross function boundary
        }
    
    }
}

Answer №1

The forEach method takes a function as an argument and iterates over each element in the array. It does not allow for breaking out of the loop prematurely. To exit from a single iteration, you can use the return statement within the function.

If you need the ability to break out of the loop entirely, you should consider using a for..of loop instead:


for(let item of itemsArray){
  if (item === 'target') {
    break;
  }
}

Answer №2

When using forEach, keep in mind that it doesn't support break statements - you'll need to use return instead.


groups = [object-A, object-B, object-C]
groups.forEach(function(group) {
  // names is also an array
  group.names.forEach(function(name) {

    if (name === 'SAM') {
      return; // exit the loop
    }
    
  });
});

Answer №3

Instead of using forEach(), you can try utilizing for loops and labeled statements in your code, similar to how it is done in JavaScript:

outer: for (const i of [1,2,3]) {
    for (const j of [4,5,6]) {
        if (j === 6) break outer
        console.log(i, j)
    }
}
console.log('done')

When executed, the above code produces the following output:

1 4
1 5
done

Feel free to experiment with this concept on the TypeScript Playground.

Answer №4

Due to my limited reputation, I am unable to leave a comment. However, after attempting Mahmoodvcs' solution, I encountered a compile error stating "Cannot find name 'name'."

The key is to declare your variable before the loop begins since it won't be automatically initialized like in a forEach loop. This may seem like a simple fix, but unforeseen issues can arise, so hopefully, this advice proves helpful to someone.

The following code snippet closely resembles the syntax of a forEach loop with the desired functionality:

for(let name of group.names){
  if (name == 'SAM') {
    break;
  }
}

In my case, there was a slight variation. I had placed a return statement inside a forEach loop, intending for it to apply to the encompassing function rather than just the forEach loop. Fortunately, no error was thrown, but discovering this post earlier saved me from potential frustration. Here's how my code evolved:

for(let x of Object.keys(this.ddlForms)) {
      if (!(!this.ddlForms[x].filterControl.value || this.ddlForms[x].filterControl.value[0] == 'All' || this.ddlForms[x].filterControl.value.some(y => y == data[this.ddlForms[x].fieldName]))) {//does not meet any of these three conditions
        return false;
      }
    }

Answer №5

For those seeking confirmation of whether "Sam" is present in the collection, leverage the .some method for a streamlined approach.

if(group.names.some(name => name == 'SAM'))
    // Implement your desired logic here.

Answer №6

Loop through the keys of the fields object and check if the value is not null, but also not an empty string. If it is, log an error message.

Answer №7

ForEach does not have support for break or return. Even though it claims to support return, it does not actually function as expected. Check out this article that provides a clear explanation on this topic. If you use ".some", it will definitely return once it finds the first item. Use .some if you need to exit the loop after finding the first item. For performing operations on each element, utilize the .forEach function.

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