ngopi.js

<script type="text/javascript">
	var arr_init = [1,2,3,'=',80,10];
	var sum_init = arr_init.reduce((total, current, index, arr) => {
		var i = arr.indexOf('=');
		
		var arr_slice = arr.slice(0, i);
		var sum = arr_slice.reduce((t, c) => t + c, 0);
		
		return sum;
	}, 0);
	
	console.log(sum_init);
</script>