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1.5.6 • Public • Published

NPM version npm module downloads per month InteractiveAdvertisingBureau


Ensures other in-page digital marketing technologies have access to CMP transparency and consent information for the IAB's Transparency and Consent Framework (TCF).


CmpApi is the only class needed to provide in-page digital marketing technologies access to a CMP transparency and consent information. The process involves setting the state of a few properties and/or a validly ecnoded TC string



npm install @iabtcf/cmpapi --save


yarn add @iabtcf/cmpapi

Create CmpApi

To create an instance of the CmpApi. Pass in your Cmp ID (assigned by IAB) and the Version (integer), and whether or not this instance is configured to use a service-specific scope to the constructor.

A custom commands object map may optionally be passed to extend the page-call functionality as well.

import {CmpApi} from '@iabtcf/cmpapi';

const cmpApi = new CmpApi(1, 3, true);

During construction of the CmpApi, the window.__tcfapi stub is replaced with CmpApi's own function for handling window.__tcfapi command requests. Commands that were waiting to be executed in the stub are filtered out if not valid. Ping and custom commands are executed and removed from the queue while all other commands remain queued until a valid TC string is set.

Note: After creation, window.__tcfapi will respond to "ping" commands and custom commands only. All other commands will be queue until update() is called for the first time.

Trigger Change Event

In the specification, events occur and registered callbacks are called "whenever the TC String is changed and a new one is available". CmpApi will trigger an event whenever update is called.

cmpApi.update(encodedTCString || '' || null);

update() may be called either an encoded TC string an empty string ('') or null.

  • Encoded TC string, CmpApi will decode the string and respond to TCData with the decoded values.
    • gdprApplies will be set to true
  • Empty string (''), CmpApi will respond to TCData with the correct structure but all primitive values will be empty.
    • gdprApplies will be set to true
  • null, CmpApi will respond to TCData with the correct structure but all primitive values will be empty.
    • gdprApplies will be set to false

CmpApi needs to know when you are going to show the user the UI to the user to recapture consent in order to set the correct eventStatus. The second parameter is a boolean letting CmpApi know that the UI is now visible to the user (it defaults to false).

Show UI – TC string needs update

// showing the ui to the user
cmpApi.update(encodedTCString, true);

/** CMP gathers user preferences */

cmpApi.update(updatedEncodedTCString, false);

Don't Show UI – TC string does not need an update

// not showing the ui to the user, only one update is needed
cmpApi.update(encodedTCString, false);

Show UI – New User – no TC string

// showing the ui to the user
cmpApi.update('', true);

/** CMP gathers user preferences */

cmpApi.update(updatedEncodedTCString, false);

GDPR doesn't apply

In the case that GDPR does not apply, simply update with null. That's all.

// only one update needed to let CmpApi that gdpr doesn't apply

Disabling the CmpApi

If, for any reason, we are unable to perform the operations in compliance with the TCF and thus should not continue to serve page request commands (other than ping), the CmpApi provides a disable method. Calling the disabled method will put the CmpApi into a permanent error state. Only ping and custom commands will continue to be executed for page requests.


Custom Commands

CmpApi has an optional parameter to pass in your map of custom commands. CmpApi will not perform any validation on custom commands. The CMP is responsible for handling validations and errors. Custom function signatures must have a callback and may define additonal params that will be passed from the calling script.


import {CmpApi} from '@iabtcf/cmpapi';

const cmpApi = new CmpApi(1, 3, false, {

  'bingo': (callback, dogName) => {

    callback(`There was a farmer who had a dog, and ${dogName} was his name-o`);


  'connectBones': (callback, startBone, endBone) => {

    callback(`The ${startBone} bone is connected to the ${endBone} bone.`);



const songLyricCallback = (lyrics, success) => {

  if(success) {


  } else {

    console.error('Error: could not get song lyrics')



__tcfapi('bingo', 2, songLyricCallback, 'Bingo');
// ouput: There was a farmer who had a dog, and Bingo was his name-o

__tcfapi('connectBones', 2, songLyricCallback, 'knee', 'thigh');
// ouput: The knee bone is connected to the thigh bone

Built-In and Custom Commands

Beginning in 1.1.0, if a custom command is defined that overlaps with a built-in command ("ping", "getTCData", "getInAppTCData", "getVendorList") then the custom command will act as a "middleware" being passed the built-in command's response and expected to pass along the response when finished.

Note: "addEventListener" and "removeEventListener" can not be overwritten. "addEventListener" utilizes the "getTCData" command, so to modify TCData responses, write a Built-In custom command for that command and both "getTCData" and "addEventListener" will utilize it. If the "removeEventListener" command is also used with a custom "getTCData" command, note that "removeEventListener" will not return tcData but rather a boolean that indicates if the listener was removed. So it is important to add a check, otherwise the CmpApi will catch that error and the callbacks will return with tcData: null.


import {CmpApi} from '@iabtcf/cmpapi';

const cmpApi = new CmpApi(1, 3, false, {

  'getTCData': (next, tcData, status) => {

     * If using with 'removeEventListener' command, add a check to see if tcData is not a boolean. */
    if (typeof tcData !== 'boolean') {

      // tcData will be constructed via the TC string and can be added to here
      tcData.reallyImportantExtraProperty = true;


    // pass data and status along
    next(tcData, status);



Note: If the next() function is not called with the TCData object, then the caller's callback will not be executed.

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