Convert ES6 Arrow Function to ES5

问题

I found a function I can use in a Leaflet project I’m working. The function is written is ES6 and it works great in both Firefox and Chrome. However, I need to target IE as well. In my research I found IE at present don't accept the ES6 Arrow function. I also I found if the ES6 function was converted to ES5, the function will work in IE. For days now I tried to convert the following function to ES5 but to no prevail. Some of the solutions I tried were found posted here. Can some please look at my script and let me know what I’m doing wrong. Also, what is the benefit of ES6 anyway; shorter script? Thank you in advance.

Here’s the working ES6 script:

points.map((p, i) => L.marker(p).bindPopup(`marker${'<strong>' + pointData[i].cityName + '</strong>' + ', ' + '</br>'  + pointData[i].discrip +  "<br /><a class='fancybox-thumb' ' style='width:150px;' rel='fancybox-button'  rel='fancybox-thumb'   data-fancybox-group='"+ pointData[i].popup +"'   title='" + pointData[i].discrip + " '  href='graphic/"+ pointData[i].popup + "' ><img src='graphic/" + pointData[i].popup + "' alt='Image' ' style='width:150px;' ></a>" + "<br/><a href='http://www.google.com'  target='_blank'>Cedellion Report</a>"}`))
.forEach(function(marker) {
    map.addLayer(marker);
    oms.addMarker(marker);
});

Here’s my best attempt/guess with no joy.

points.map(function(p, i) {
L.marker(p).bindPopup(`marker${'<strong>' + pointData[i].cityName + '</strong>' + ', ' + '</br>'  + pointData[i].discrip +  "<br /><a class='fancybox-thumb' ' style='width:150px;' rel='fancybox-button'  rel='fancybox-thumb'   data-fancybox-group='"+ pointData[i].popup +"'   title='" + pointData[i].discrip + " '  href='graphic/"+ pointData[i].popup + "' ><img src='graphic/" + pointData[i].popup + "' alt='Image' ' style='width:150px;' ></a>" + "<br/><a href='http://www.google.com'  target='_blank'>Cedellion Report</a>"}`)})
.forEach(function(marker) {
map.addLayer(marker);
oms.addMarker(marker);
});

回答1:

When you have ES6+ code that you want to make compatible for ES5, to transpile the syntax, you can do it automatically with a transpiler like Babel. Plugging in your code gives this result:

points.map(function (p, i) {
  return L.marker(p).bindPopup("marker" + ('<strong>' + pointData[i].cityName + '</strong>' + ', ' + '</br>' + pointData[i].discrip + "<br /><a class='fancybox-thumb' ' style='width:150px;' rel='fancybox-button'  rel='fancybox-thumb'   data-fancybox-group='" + pointData[i].popup + "'   title='" + pointData[i].discrip + " '  href='graphic/" + pointData[i].popup + "' ><img src='graphic/" + pointData[i].popup + "' alt='Image' ' style='width:150px;' ></a>" + "<br/><a href='http://www.google.com'  target='_blank'>Cedellion Report</a>"));
}).forEach(function (marker) {
  map.addLayer(marker);
  oms.addMarker(marker);
});

You needed to transpile the template literal too - declare strings and concatenate with + instead of using ${} syntax. In addition, you needed to return the L.marker... from the .map callback.

Note that this only transpiles syntax, not methods - if you're using ES6+ methods (for example, Array.prototype.includes), Babel won't be enough - you'll either need to change the code manually to use an ES5 method (like indexOf), or, a better option, include a polyfill (example) to define the ES6+ methods on clients viewing your page.

回答2:

If an arrow function is simply returning a single line of code, you can omit the statement brackets and the return keyword. This tells the arrow function to return the statement.

So, just add return statement and it should work

for more info: https://codeburst.io/javascript-understand-arrow-function-syntax-ab4081bba85b

来源：https://stackoverflow.com/questions/55309225/convert-es6-arrow-function-to-es5

标签

javascript

ecmascript-6

leaflet