Conditionally modifying array elements
JavaScriptAll snippets in this category →
Posted on If we want to change only the values in an array that match a condition, we can combine Array.prototype.map() with a ternary operator. By putting these in a function, we can quickly apply this pattern to many different scenarios.
// takes an array, a function that checks each element, and another function
// that it applies to every element that the check returns `true` for
const mapMatches = (array, checkFunction, changeFunction) =>
array.map(element => checkFunction(element) ? changeFunction(element) : element)
// change every name that contains an “e” into uppercase
mapMatches(
["Leo", "Paul", "Joe", "Fred", "Sam"],
name => name.includes("e"),
name => name.toUpperCase()
)
// ⇒ ["LEO", "Paul", "JOE", "FRED", "Sam"],
// divide every even number by two
mapMatches(
[4, 8, 15, 16, 23, 42],
number => number % 2 === 0,
number => number / 2
)
// ⇒ [2, 4, 15, 8, 23, 21]// takes an array, a function that checks each element, and another function
// that it applies to every element that the check returns `true` for
const mapMatches = (array, checkFunction, changeFunction) =>
array.map(element => checkFunction(element) ? changeFunction(element) : element)
// change every name that contains an “e” into uppercase
mapMatches(
["Leo", "Paul", "Joe", "Fred", "Sam"],
name => name.includes("e"),
name => name.toUpperCase()
)
// ⇒ ["LEO", "Paul", "JOE", "FRED", "Sam"],
// divide every even number by two
mapMatches(
[4, 8, 15, 16, 23, 42],
number => number % 2 === 0,
number => number / 2
)
// ⇒ [2, 4, 15, 8, 23, 21]// takes an array, a function that checks each element, and another function
// that it applies to every element that the check returns `true` for
const mapMatches = (array, checkFunction, changeFunction) =>
array.map(element => checkFunction(element) ? changeFunction(element) : element)
// change every name that contains an “e” into uppercase
mapMatches(
["Leo", "Paul", "Joe", "Fred", "Sam"],
name => name.includes("e"),
name => name.toUpperCase()
)
// ⇒ ["LEO", "Paul", "JOE", "FRED", "Sam"],
// divide every even number by two
mapMatches(
[4, 8, 15, 16, 23, 42],
number => number % 2 === 0,
number => number / 2
)
// ⇒ [2, 4, 15, 8, 23, 21]// takes an array, a function that checks each element, and another function
// that it applies to every element that the check returns `true` for
const mapMatches = (array, checkFunction, changeFunction) =>
array.map(element => checkFunction(element) ? changeFunction(element) : element)
// change every name that contains an “e” into uppercase
mapMatches(
["Leo", "Paul", "Joe", "Fred", "Sam"],
name => name.includes("e"),
name => name.toUpperCase()
)
// ⇒ ["LEO", "Paul", "JOE", "FRED", "Sam"],
// divide every even number by two
mapMatches(
[4, 8, 15, 16, 23, 42],
number => number % 2 === 0,
number => number / 2
)
// ⇒ [2, 4, 15, 8, 23, 21]