如何检查javascript数组是否持有具有特定值的属性，如果是，则返回true

Question

I have a select - option in angular, and I need to check values that have same id as id in database, so I have tried something like this:

isDropdownValueSelected(amf: ApplicationModuleForm): boolean {
    for (let i = 0; i < this.role.applicationForms.length; i++) {
      if (this.role.applicationForms[i].id == amf.id) {
        return true;
      }
      else {
        return false;
      }
    }
 }

My angular part:

<div class="col-lg-9">
     <select id="applicationModuleFormSelect" name="applicationModuleFormSelect" class="form-control multiselect-select-all" multiple="multiple" data-fouc>
        <option *ngFor="let amf of appModuleForms;" [value]="amf.id" [selected]="isDropdownValueSelected(amf)">{{amf.title}}</option>
     </select>
</div>

So basically there I wanted to loop for each id in option and if I found similar in my array I would return true, because array this.role.applicationForms holds values from database, but unfortunatelly this does not works, nothing is selected in dropdown and I tested with console log it says only 1 value exist even if there are 3..

Thanks guys Cheers

Answer 1

Maybe you need to move the false value to the end for returning, because every return statement ends the function.

isDropdownValueSelected(amf: ApplicationModuleForm): boolean {
    for (let i = 0; i < this.role.applicationForms.length; i++) {
        if (this.role.applicationForms[i].id == amf.id) {
            return true;
        }
    }
    return false;
}

Answer 2

This function only works when the id of the first element is matched, because you're returning the value on every check.

You should update the code to be like this:

isDropdownValueSelected(amf: ApplicationModuleForm): boolean {
    for (let i = 0; i < this.role.applicationForms.length; i++) {
        if (this.role.applicationForms[i].id == amf.id) {
            return true;
        }
    }
    return false;
}

Answer 3

Assuming applicationForms is an array, you can use the method some :

isDropdownValueSelected(amf: ApplicationModuleForm): boolean {
  return this.role.applicationForms.some(({id}) => id === amf.id);
}

Answer 4

Use the some operator instead of looping on your elements:

isDropdownValueSelected(amf: ApplicationModuleForm): boolean {
    return this.role.applicationForms.some(e => e.id === amf.id);
}

Answer 5

You do not need for loop:

isDropdownValueSelected(amf: ApplicationModuleForm): boolean {
            if (this.role.applicationForms.find(x => x.id == amf.id)) {
                return true;
            }
            else {
                return false;
            }
        }