I needed to transform dates in an HTML file to be in "MMM YYYY" format without using any dependencies. This is how I did it using vanilla JS. This can be pasted directly into a dev-tools console to test.

minified.js

const dateFields=document.getElementsByClassName("blog-date"),monthNames=["January","February","March","April","May","June","July","August","September","October","November","December"],transformDate=e=>{const t=new Date(e.innerHTML);return`${t.getDate()} ${monthNames[t.getMonth()]} ${t.getFullYear()}`};dateFields.forEach(e=>{e.innerHTML=transformDate(e)});

transformSquarespaceBlogDateFields.js

const dateFields = document.getElementsByClassName("blog-date");

const monthNames = ["January", "February", "March", "April", "May", "June",
  "July", "August", "September", "October", "November", "December"
];

const transformDate = (htmElem) => {
  const newDate = new Date(htmElem.innerHTML);
  return `${newDate.getDate()} ${monthNames[newDate.getMonth()]} ${newDate.getFullYear()}`;
}

dateFields.forEach((htm) => {
  htm.innerHTML = transformDate(htm);
});