[Feature] Allow providing your own implementation of fetch

[opepin]

Allow providing your own implementation of fetch by delaying caching from instanciation to first call.

Fetch can now be instrumented for performance monitoring/error or data capture. https://docs.logrocket.com/docs/troubleshooting-sessions#network-requests-are-missing-or-not-being-recorded

[salesforce-cla]

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[joeluong-sfcc]

Hi @opepin, thanks for creating this PR. Would you be willing to provide some documentation/example on how you would pass in a custom implementation of a fetch call and adding a unit test?

[opepin]

I don't have a unit test, but the idea would be to override the window.fetch method :

const { fetch: originalFetch } = window;

window.fetch = async (...args) => {
let [resource, config ] = args;
console.log('request interceptor before')
const response = await originalFetch(resource, config);
console.log('request interceptor after')
return response;
};

before calling the api

[opepin]

fixes #159