Iain Freestone

💬 Create well-formatted console.log() messages using string substitution

May 25, 2020

Use string substitutions tokens in your console.log() calls to create well-formatted messages.

Each substitute string (%o - object, %s - string, %d - integer, %f - floating point value ) in the message will pull in the next argument of the console.log(msg,arg1,arg2).

For example, the following example will pull in the String “Iain”, followed by the String “Freestone” and finally the integer 39

console.log(“User %s %s is %d years old.”,“Iain”,“Freestone”,39)

Outputing - “User Iain Freestone is 39 years old.”

let users = [
  {
    firstname: "Joe",
    lastname: "Bloggs",
    age: 45,
  },
  {
    firstname: "Jane",
    lastname: "Doe",
    age: 34,
  },
]

users.map(user =>
  console.log(
    "User %s %s is %d years old.",
    user.firstname,
    user.lastname,
    user.age
  )
)

// User Joe Bloggs is 45 years old.
// User Jane Doe is 34 years old.