Javascript set const variable inside of a try block

Declaring a variable as const requires you to immediately point it to a value and this reference cannot be changed.

Meaning you cannot define it at one place (outside of try) and assign it a value somewhere else (inside of try).

const test; // Syntax Error
try {
  test = 5; 
} catch(err) {}

On the other hand, both creating it and giving it a value within the try block is fine.

try {
  const test = 5; // this is fine
} catch(err) {}

However, const is block-scoped, like let, so if you do create it and give it a value within your try block, it will only exist within that scope.

try {
  const test = 5; // this is fine
} catch(err) {}
console.log(test); // test doesn't exist here

Therefore, if you need to access this variable outside of the try, you must use let:

let configPath;
try {
   configPath = path.resolve(process.cwd(), config);
} catch(error) {
    //.....   
}

console.log(configPath);

Alternatively, although probably more confusingly, you can use var to create a variable within the try and use it outside of it because var is scoped within the function, not the block (and gets hoisted):

try {
   var configPath = path.resolve(process.cwd(), config);
} catch(error) {
    //.....   
}

console.log(configPath);

'use strict';

const path = require('path');

const configPath = (function() {
  try {
    return path.resolve(process.cwd(), config);
  } catch (error) {
    //.....
  }
})()

console.log(configPath);

I would try to use a temp variable with let and assign that to a const var after the try/catch and 'delete' the temp var.

'use strict';

let temp;
try {
  temp = path.resolve(process.cwd(), config);
} catch (error) {
  //.....   
}

const configPath = temp;
temp = undefined;

console.log(configPath);

You can avoid the try block altogether if the function is async! Just learned this today, thought I'd share!

More broadly applicable to just your situation as this is the top Google result for "const in a try block"

'use strict';
const path = require('path');

const getPath = async () => {
    return path.resolve(process.cwd())
}

const logPath = async () => {
    const configPath = await getPath().catch(e => console.log(e)) <--avoid the try
    console.log(configPath);
}

logPath()

Works great when you're already in an async function and need to wait for something else:

async function main() {
  const result = await asyncTask().catch(error => console.error(error));
}

Learned from: https://stackoverflow.com/a/55024396/2936521

There are plenty of good answers here. But it's real annoying to have to manage your lets being inside and out of scope. So if you are like me, and came here searching for a better pattern. I wrote a little utility that helps a ton.

export const tc = <T>(option: { try: () => T; catch: (e: Error) => T }) => {
  try {
    return option.try()
  } catch (e) {
    return option.catch(e)
  }
}

Here are some unit tests to show how it's useful

import { tc } from './tc'
describe('tc', () => {
  it('should return successfully', () => {
    const result = tc({
      try: () => 1 + 2,
      catch: () => -1,
    })
    expect(result).toEqual(3)
  })
  it('should catch', () => {
    const spy = jest.fn()
    const result = tc({
      try: (): number => {
        throw new Error('Test')
      },
      catch: (e) => {
        spy()
        expect(e.message).toEqual('Test')
        return -1
      },
    })
    expect(spy).toHaveBeenCalledTimes(1)
    expect(result)
  })
  it('should rethrow', () => {
    expect(() =>
      tc({
        try: (): number => {
          throw new Error('Test')
        },
        catch: (e) => {
          throw e
        },
      }),
    ).toThrowError()
  })
  it('should have proper types', () => {
    // @ts-expect-error
    const result: string = tc({
      try: () => 12,
      catch: (e) => {
        return -1
      },
    })
  })
})