Question

Question

Although you can explicitly check if a value is true or false, it’s a convention in JavaScript to test against all falsy values. For example, we can test if a variable value is falsy by testing if (value).

Code

function UnconventionalDefaults(params, defaultParams) {
  if (params === undefined) {
    params = defaultParams;
  }

  // function would do work here

  return params;
}

// Modify this function to set params to defaultParams if params
// is falsy
function moreConventionalDefaults(params, defaultParams) {
  // do a more conventional check here (check if params is falsy, 
  // and not just undefined
  if(params === undefined){
    params === defaultParams;
  }else if(params === null){
    params === defaultParams;
  }else if(params === ""){
    params === defaultParams;
  }else if(params === false){
    params === defaultParams;
  }

  return params;
}

Although I’m testing against all the falsy values, this code is not being accepted. What is it that I’m doing wrong? Is there a better way to do it?

Answer 1

• You cannot use === for assigning into params. Use = instead.

• Also those are not all falsy values, you are missing 0 and NaN.

The whole method can be simplified into:

function moreConventionalDefaults(params, defaultParams) {
  return params || defaultParams;
}

params will be evaluated and if it is falsy then the defaultParams will be returned.

EDIT: Have a loot at great article Exploring JavaScript’s Logical OR Operator by Addy Osmani for more information.