Validate that the input is an array

Question

Validate that the input is an array

Looking for a way to determine if a function parameter is an array or not, and then process it accordingly. If the parameter is not an array, convert it into an array before performing the desired function.

For example:

interface employee {
    first: string,
    last: string
}

function updateEmployees (emp: employee | employee[]) {
    let employees = [];
    if (emp instanceof Array) employees = [emp];
    else employees = emp;
    employees.forEach(function(e){
        return 'something'
    })
}

While this logic seems correct, it's raising a warning stating

Type 'employee' is not assignable to type 'any[]'. Property 'length' is missing in type 'employee'.

javascript arrays typescript

Answer 1

Answer №1

Check out the revised version of your code:

function updateStaff (staff: employee | employee[]) {
    let employees: employee[] = [];
    if (Array.isArray(staff)) employees = staff;
    else employees = [staff];
    employees.forEach(function(e){
        return 'something'
    })
}

Alternatively, you can make it more concise:

function updateStaff(staff: employee | employee[]) {
    (Array.isArray(staff) ? staff : [staff]).forEach(function(e){
        return 'something'
    })
}

Answer 2

Check out the revised version of your code:

function updateStaff (staff: employee | employee[]) {
    let employees: employee[] = [];
    if (Array.isArray(staff)) employees = staff;
    else employees = [staff];
    employees.forEach(function(e){
        return 'something'
    })
}

Alternatively, you can make it more concise:

function updateStaff(staff: employee | employee[]) {
    (Array.isArray(staff) ? staff : [staff]).forEach(function(e){
        return 'something'
    })
}

Answer 3

Answer №2

Here is a function in Typescript that ensures an array is returned safely. It checks for null or undefined items and returns an empty array if found.

function safeArray<T>(value: T | T[]): T[] {
  if (Array.isArray(value)) {
    return value
  } else if (value === undefined || value === null) {
    return []
  } else {
    return [value]
  }
}

If you want to include null or undefined items:

function safeArray<T>(value: T | T[]): T[] {
  if (Array.isArray(value)) {
    return value
  } 
  else {
    return [value]
  }
}

Usage example:

function updateEmployees(emp: employee | employee[]) {
    safeArray(emp).forEach(function(e){
        return 'something'
    })
}

The additional check prevents runtime errors when encountering null or undefined elements, ensuring the loop iterates only over 'employees'.

Answer 4

Here is a function in Typescript that ensures an array is returned safely. It checks for null or undefined items and returns an empty array if found.

function safeArray<T>(value: T | T[]): T[] {
  if (Array.isArray(value)) {
    return value
  } else if (value === undefined || value === null) {
    return []
  } else {
    return [value]
  }
}

If you want to include null or undefined items:

function safeArray<T>(value: T | T[]): T[] {
  if (Array.isArray(value)) {
    return value
  } 
  else {
    return [value]
  }
}

Usage example:

function updateEmployees(emp: employee | employee[]) {
    safeArray(emp).forEach(function(e){
        return 'something'
    })
}

The additional check prevents runtime errors when encountering null or undefined elements, ensuring the loop iterates only over 'employees'.

Validate that the input is an array

Answer №1

Answer №2

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