/* get reference to the canvas */
const canvas = document.getElementById("svg_canvas");
/* setup an object with the attributes for each element we want to set */
const elements = [{
  name: "square1",
  type: "rect",
  textContent: "mouse over",
  attributes: {
    id: "square1",
    "data-target": "toggle-target",
    x: 100,
    y: 100,
    width: 100,
    height: 100,
    fill: "blue",
    class: "hovering-sq"
  }
}, {
  name: "happytext",
  type: "text",
  textContent: "mouse over",
  attributes: {
    x: 110,
    y: 150,
    fill: "cyan",
    class: "toggle-target"
  }
}, {
  name: "square2",
  type: "rect",
  attributes: {
    id: "square2",
    x: 50,
    y: 50,
    width: 50,
    height: 50,
    fill: "red",
    class: "target-sq hide toggle-target"
  }
}, {
  name: "textthing",
  type: "text",
  textContent: "howdy doodee",
  attributes: {
    id: "textthing",
    x: 200,
    y: 200,
    fill: "green",
    class: "hide me toggle-target"
  }
}];
/* now using the object above create an element with the attributes */
elements.forEach((prop) => {
  let el = document.createElementNS('http://www.w3.org/2000/svg', prop.type);
  const attributes = prop.attributes;
  if (prop.hasOwnProperty('textContent')) {
    el.textContent = prop.textContent;
  }
  for (const attr in attributes) {
    el.setAttribute(attr, attributes[attr]);
  }
  canvas.appendChild(el);
});
/* get the element we want to use for the mouse enter/leave */
const t = canvas.querySelector('.hovering-sq');
/* handle the event for enter/leave */
function handleEvent(event) {
  const container = event.target.closest('svg');
  const targets = container.dataset.toggletargets;
  const hiders = container.querySelectorAll(targets);
  hiders.forEach((el) => {
    el.classList.toggle('hide');
  });
}
/* set up the event handlers */
t.addEventListener('mouseenter', handleEvent);
t.addEventListener('mouseleave', handleEvent);

.hide {
  display: none;
}

<svg id="svg_canvas" viewBox="0 0 1200 600" width="1200px" height="600px" xmlns="http://www.w3.org/2000/svg" data-toggletargets=".toggle-target"></svg>