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6.0.0 • Public • Published

FAST Web utilities

This package is a collection of utilities intended to be used for web projects.


npm i --save @microsoft/fast-web-utilities


DOM utilities


The getKeyCode function gets the numeric key code associated with a keyboard event. This method is for use with DOM level 3 events that still use the deprecated keyCode property.

import { getKeyCode } from "@microsoft/fast-web-utilities";

handleKeyPress = (e) => {
    let keyCode = getKeyCode(e);

    // Do something based on keyCode value

HTML utilities


The getClientRectWithMargin function gets the client bounding rectangle including any margins of an element.

import { getClientRectWithMargin } from "@microsoft/fast-web-utilities";

const itemWidth = getClientRectWithMargin(item).width;
const itemHeight = getClientRectWithMargin(item).height;


The convertStylePropertyPixelsToNumber function will convert a property value from an elements computed style from pixels to a number value.

import { convertStylePropertyPixelsToNumber } from "@microsoft/fast-web-utilities";

const elementTopMargin = convertStylePropertyPixelsToNumber(style, "margin-top");

Key utilities

Key strings

Commonly used event.key values are available as individual exports. Additional key values will be added as needed.

import { keyEnter, keySpace } from "@microsoft/fast-web-utilities";

handleKeyPress = (e) => {
    switch (e.key) {
        case keySpace:
        case keyEnter:
            // Do something if key matches

KeyCodes (enum)

Keycodes are deprecated and their use should be avoided. Use the individual string key values instead.

Localization utilities

Typescript enum

The Direction enum contains the ltr and rtl enum for use in a Typescript project.

import { Direction } from "@microsoft/fast-web-utilities";

let direction: Direction = Direction.ltr;

Number utilities


The limit function ensures that a value is between a min and max value. If the value is lower than min, min will be returned. If the value is greater than max, max will be retured.

import { limit } from "@microsoft/fast-web-utilities";
const incomingNumber; // 11 
const setNumberByLimit = limit(0, 10, incomingNumber); // returns 10


The wrapInBounds function keeps a given value within the bounds of a min and max value. If the value is larger than the max, the minimum value will be returned. If the value is smaller than the minimum, the maximum will be returned. Otherwise, the value is returned un-changed.

import { wrapInBounds } from "@microsoft/fast-web-utilities";
const slides; // 5
const index; // 5
const activeIndex = wrapInBounds(0, this.slides.length - 1, index) // returns 0

String utilities


The format function builds a string from a format specifier and replacement parameters.

import { format } from "@microsoft/fast-web-utilities";

const formatterString = "View {0} {1}";

const newString = format(formatterString, "page", "4")); // "View page 4"


The startsWith function checks to see if one string starts with another. The function is case sensitive.

import { startsWith } from "@microsoft/fast-web-utilities";

const matchIsFalse = startsWith("HelloWorld", "World"); // false
const matchIsTrue = startsWith("HelloWorld", "Hello"); // true


The isNullOrWhiteSpace function determines if the specified string is undefined, null, empty, or whitespace. The function returns true if the value is undefined, null, empty, or whitespace, otherwise false.

import { isNullOrWhiteSpace } from "@microsoft/fast-web-utilities";

const myAnchor = document.querySelector("#id");
const checkWhitespace = isNullOrWhiteSpace(myAnchor.href);


The pascalCase function converts a string to Pascal Case

import { pascalCase } from "@microsoft/fast-web-utilities";

const hyphenatedToPascal = pascalCase("my-string");
const uppercaseToPascal = pascalCase("MY STRING");
const whitespaceToPascal = pascalCase(" my string ");


A utility for merging class names into a single string conditionally. Accepts any number of strings, functions that return strings and two index arrays where the first index is a string or function that returns a string, and the second index is a boolean.

import { classNames } from "@microsoft/fast-web-utilities";

// evaluates to "classOne classTwo classThree classFive"
const myJoinedClassNames = classNames(
    () => "classTwo",
    ["classThree", true],
    ["classFour", false]
    [() => "classFive", true],
    [() => "classSix", false]




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