LWC - Calling Javascript method from static resource 3rd party JS file [duplicate]

Question

I have following JS file uploaded as static resource in Salesforce.

Static resource utility.zip / utility.js file

var x = function (a, b) {return a * b};

I would like to call function variable from static resource JS file from LWC component.

    import { loadScript, loadStyle } from 'lightning/platformResourceLoader';
    import utility from '@salesforce/resourceUrl/utility';

    export default class lwccomponent extends LightningElement {

     renderedCallback() {

        Promise.all([
            loadScript(this, utilities + '/utility.js')
        ])
            .then(() => {
                alert('loaded');
                /* how can i call method / function variable from JS file , i am unable to do it. */
            })
            .catch(error => {
                this.dispatchEvent(
                    new ShowToastEvent({
                        title: 'Error loading JS file',
                        message: error.message,
                        variant: 'error'
                    })
                );
            });

    }
}

my objective is to create a common set of functions to share among components/ project to have to prevent any data issues.

Answer 1

If you want to develop code, that will be shared with lwc components, create lwc service component. Commonly, js is loaded as a static resource for already existed 3-party js libraries, but if you don't have any options except grouping js code in static resource, your js code should follow the following rule: must explicitly attach library global to window

window.myLib = (function() {
    return {
        myFunction: function(a, b) {
            return a * b;
        }
    };
}());

then you can call it like:

loadScript(this, utilities + '/utility.js').then(() => {
    let result = myLib.myFunction(2,2);
});

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you can check rest of requirements for the compatible js library with locker service in this question